Collineation measurement a method for constructing the imperial citadel of thang long in harmony with nature

+ MODEL Frontiers of Architectural Research xxx (xxxx) xxx Available online at www.sciencedirect.com ScienceDirect journal homepage: www.keaipublishing.com/foar RESEARCH ARTICLE Collineation measurement: A method for constructing the imperial citadel of Thang Long in harmony with nature Theanh Dinh a,b,c, Xiaogeng Ren a,b,* a School of Architecture, Southeast University, Nanjing, China VNU School of Interdisciplinary Studies, Vietnam National University, Hanoi, Vietnam c Institute of Imperial Citadel Studies of the Vietnam Academy of Social Sciences, Hanoi, Vietnam b Received 16 February 2022; received in revised form April 2022; accepted 27 April 2022 KEYWORDS Human settlement; Collineation measurement; Shan-shui structure; Vietnamese ancient capitals; The imperial citadel of Thang long Abstract The Imperial Citadel of Thang Long is a crucial case in ancient Vietnam’s planning and design history Although historical materials indicate that the orientation of the Imperial Citadel of Thang Long has a dialectical unity relationship with the surrounding mountains, current research is only speculative generalization and lacks empirical analysis Based on existing findings, this paper identifies the collineation measurement as a general method in the Sinosphere countries for determining spatial orientation Using a mixed-method of historical archives, fieldwork and simulation model, this paper summarizes historical clues and three design perspectives related to spatial orientation by statistical analysis Further, it analyzes the logic and application of collineation measurement in constructing the Imperial Citadel of Thang Long The results show that Vietnamese designers used Tản Vie ˆn Mountain as a component of Thang Long city by collineating the two mountain peaks to the west Tản Vie ˆn Mountain and the highlands extending eastward from it are used as the key to establishing the position of the Imperial Citadel, setting the spatial structure of human settlements, and the development of city space The location, layout, and form of important buildings in the Imperial Citadel are also closely related to the surrounding landscape within 50 km ª 2022 Higher Education Press Limited Company Publishing services by Elsevier B.V on behalf of KeAi Communications Co Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction The ancient name for contemporary Hanoi is Thang Long Vietnamese dynasties, such as Ly ´ (1010e1225), Trần * Corresponding author E-ma il a ddresses: theanhdinh@vnu.edu.vn (T Dinh), renxiaogeng@126.com (X Ren) Peer review under responsibility of Southeast University (1225e1400), Le ˆ (1428e1527), Mạc (1527e1592), and Le ˆ Trung Hưng (1592e1789), had their regional political and cultural ng Long (Phan, 2010b) The Imperial Citadel of centres at Tha Thang Long’s core sector, which includes the citadel structures and the remnants of the 18 Hoang Dieu ancient sites, was designated as a World Heritage Site on July 31, 2010, under the https://doi.org/10.1016/j.foar.2022.04.010 2095-2635/ª 2022 Higher Education Press Limited Company Publishing services by Elsevier B.V on behalf of KeAi Communications Co Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article as: T Dinh and X Ren, Collineation measurement: A method for constructing the imperial citadel of Thang Long in harmony with nature, Frontiers of Architectural Research, https://doi.org/10.1016/j.foar.2022.04.010 + MODEL T Dinh and X Ren name Imperial Citadel of Thang Long.1 Many Vietnamese and non-Vietnamese academics have studied the Imperial Citadel’s structures and urban form (Kazuto, 2010; Bu `i and Tống, 2010; Phạm, 2013; Momoki, 2010; Vu and Vu, 2007) As archaeological work progressed between 2002e2004 and 2008e2009, Vietnamese archaeologists have excavated numerous building foundations dating back to the Ly Dynasty on the site of the Imperial Citadel of Thang Long Archaeological investigations showed that the general structure of the remains exhibited a phenomenon of uniform orientation (Bu `i and Tống, 2010, pp 28, 34) The palaces, gates, and ceremonial routes were all oriented along an azimuth of 185 (true north-based azimuths, with north being 0 ) (Fig 1) (Bu `i and Tống, 2010, pp 28,33; Kazuto, 2010, p 42) Inoue Kazuto (2010, pp 69e70) concluded that the Imperial Citadel of Thang Long’s platform included the idea of an orientation system According to Phạm Le ˆ Huy (2018, p 82), the citadel’s orientation was most likely decided during design and construction by referencing the layout, architectural forms, and other characteristics of Bianjing (now Kaifeng), the Northern Song Dynasty capital city There are still two questions which have not been solved: (1) Although the Imperial Citadel of Thang Long’s spatial orientation system seems to be very apparent from the excavated site, extant studies are primarily speculative and deficient in the empirical examination;(2) Existing historical materials indicate that the orientation of the Imperial Citadel of Thang Long has a dialectical unity relationship with the surrounding mountains, which is defined in this paper as the issue of city-mountain relationship However, current research has not yet provided a reasonable explanation for this issue In other words, there has been very little research that offers a thorough examination of the spatial orientation and design process of the Imperial Citadel of Thang Long This paper highlights that the approach of collineation measurement is the key to a thorough understanding of the spatial orientation design and its process of the Imperial Citadel of Thang Long Three main historical clues serve as the basis of this research: (1) The history of Sino-Vietnamese exchanges in the 11th-century showcase that the theory and methods of constructing capital cities in ancient Vietnam were in line with those of the Tang-Song period Chinese literature, such as Yu Hai (玉海) and Song Shi (宋史), recorded in detail that the Vietnamese emperor in the 11th century requested the Nine Classics from the Northern Song court and was granted permission by the Northern Song emperor.2 The so-called Nine Classics is the collective name for the nine Confucian classics, of which books such as Zhou Li - Kaogong Ji (周礼$考工记) and Li Ji - Ming Tang Wei (礼记$ 明堂位), and Yue Ling(月令) documented much about the techniques used to build the royal cities and establish their orientations (2) Vietnamese archaeologists unearthed a Tang-style ’dougong’ (dated to the 11th century) on the ruins of the Imperial Citadel of Thang Long (Bu `i, 2015, p 20) Through the architectural analysis of excavated building foundations, archaeology has identified the Northern Song architectural ruler (a ruler of 0.299 m in length) as the key to the construction of the palace, courtyard, roads, and city walls of the Imperial Citadel (Kazuto, 2010, p 45) (3) Many scholars demonstrated that the collineation measurement approach effectively analyzes the orientation of ancient capital cities and resolves mountain-city relationships (see Sect 2.2 below for details) However, contemporary research mainly focused on Chinese capital cities, with an absence of studies on ancient Vietnamese capital cities Based on the cultural exchanges between China and Vietnam in the 11th century, it is necessary to examine the design method and process of the Imperial City of Thang Long to understand the city-mountain relationship fully in a more extensive perspective of East Asia This paper presents more expansive thinking on archaeology, architectural and planning histories of Thang Long, and a deeper understanding of the perception of its heritage value Additionally, it could compare historical capitals with East Asian nations and offer a solid foundation for urban morphology Materials and methods 2.1 Materials This paper uses raw archives from the National Library of Vietnam, the Institute of Sino-Nom Studies, and the Chinese Text Project With the information of text, authorship, date, and provenance, the historical materials used were subjected to a thorough investigation by the imperial court of the period Therefore, their substance had some credibility Four categories of historical materials serve as the main sources: first are the royal chronicles, such as The concise summary of the Vietnamese historical records (越史略, hereafter, Concise summary) (the 1370s)3 and The complete book of the historical records of Ðại Việt (大越史記全書, hereafter, Complete book) (1479).4 Second are the royal geographical historical materials, such as Atlas of Hongduc (洪 德版圖冊) (1490),5 Descriptive Geography of Việt Kingdom (皇 越地輿誌) (1806),6 Dai Nam Comprehensive Encyclopaedia (大 南一統志) (1882),7 The Descriptive Geography of the Emperor The concise summary of the Vietnamese historical records [Việt Sử Lược 越史略] is a historical text that was compiled during the Trần Dynasty The 3-vol book was finished around 1377 and covered the history of Vietnam from the reign of Triệu Ða ` to the collapse of the Ly ´ Dynasty The complete book of the historical records of Ðại Việt [Ðại Việt Sử Ky `n Thư 大越史記全書] is the official national chronicle of ´ Toa the Vietnamese state, that was originally compiled by the royal historian Ngo ˆ S~ı Lie ˆn under the order of the Emperor Le ˆ Tha ´nh To ˆng and was finished in 1479 during the Le ˆ period Atlas of Hongduc [Hồng Ðức Bản Ðồ Sa ´ch 洪德版圖冊], sometimes called the Geography of Hồng Ðức, is a set of geographic maps of Dai Viet issued during the reign of Le ˆ Tha ´nh To ˆng, the 21st year of Hồng Ðức era (1490) Descriptive Geography of Việt Kingdom [Hoa `ng Việt Ðịa Dư Chı´皇越地輿誌] is one of the earliest official geographical gazetteers of the Nguyễn dynasty, written in the fifth year of the Gia Long era (1806) ^´ Dai Nam Comprehensive Encyclopaedia [Ðại Nam Nha ˆt Thống Chı´大南一統志] is the official geographical record of Vietnam’s Nguyễn dynasty written in chữ Han compiled in the late nineteenth century It also contains historical records of military campaigns UNESCO., 2010 Central Sector of the Imperial Citadel of Thang Long e Hanoi https://whc.unesco.org/en/list/1328 ‘四年七月賜交趾九經, 從其請也’ in The Yuhai [Jade ocean] Volume 55; ’乙亥、交州來貢、賜黎龍廷九經及佛氏書’ in the Song Shi[The History of Song] Volume + MODEL Frontiers of Architectural Research xxx (xxxx) xxx Fig Map of the centre of Thang Long Imperial Citadel Archaeological Site Source: Institute of Imperial Citadel Studies (IICS) Dong Khanh (同慶地輿志) (1889),8 and Complete Atlas of the Ðại Việt Kingdom (大越地舆全编) (1900).9 Third comes historical poetry, such as Selected Collections of Cao Ba´ Qua´’ s Chinese Poetry (高伯适汉诗选) Fourth are the contemporaneous materials from other Sinosphere countries that record relevant techniques for determining the orientation of palace cities, such as Ten Computational Canons (算经十书) (1084),10 Khanbaliq Capital Rhapsody (大都赋) (1298),11 and The stele of reconstruction of Qiyin Temple in Yangshan (重修仰山栖隐 寺碑记) (1459) We also utilised information from archaeological excavations, topography, and geology The archaeological excavation data obtained from the field archaeological reports from the Institute of Imperial Citadel Studies and the Institute of Archaeology A 1:5000 scale topographic map of Hanoi for 2018 from the Hanoi Urban Planning Institute12 and 90 m DEM digital elevation data from the CGIAR-CSI online database make up the topographic data.13 The geological survey report of the Institute of Geophysics’ borehole provides the geological data (Bu `i and Nguyễn, 2015) The Descriptive Geography of the Emperor Ðồng Kha ´nh [Ðồng Kha ´nh Ðịa Dư Chı´ 同慶地輿志] is an important document of the Nguyễn dynasty, and is regarded nowadays as the final work in the bibliography of classical Vietnamese geography Complete Atlas of the Ðại Việt Kingdom [Ðại Việt Ðịa Dư Toa `n Bie ˆn 大越地舆全编] introduces the history of Vietnam from the 10th century B.C to the Nguyen dynasty, including administration division, mountains and rivers, and citadels 10 The Ten Computational Canons [算经十书] was a collection of ten Chinese mathematical works, compiled by early Tang dynasty mathematician Li Chunfeng (602e670), as the official mathematical texts for imperial examinations in mathematics The government of the Song dynasty actively promoted the study of mathematics There were two government xylograph editions of The Ten Computational Canons in 1084 and 1213 11 Li Weisun’s Khanbaliq Capital Rhapsody [大都赋], introduces the information of the mountains around Beijing, showing the geography of the capital from near to far as multiple perils protect it 12 Hanoi City Committee Hanoi Urban Planning Institute, http:// vqh.hanoi.gov.vn/en 13 Data was obtained from Climate Change, Agriculture and Food Security, Consortium for Spatial Information (CGIAR-CSI) online database, https://srtm.csi.cgiar.org + MODEL T Dinh and X Ren Geographic Information System (GIS) platform and Landscape Information Modeling(LIM) Moreover, the fieldwork method has also been used to restore and verify findings The second step is an exclusion or identification of statistical analysis findings Third, the paper concludes with a summary of the logic and techniques used to construct the Thang Long City and establish the orientation of the Imperial Citadel Further, it discusses the planning ideology behind this process in harmony with nature The extensive research available on Hanoi’s geomorphology, water network, and urban history demonstrates that the geomorphology around the Imperial Citadel of Thang Long has changed little between the 11th century and the present.14 To reconstruct the historical geomorphology, we utilised data from 29 archaeological sites in the Hanoi area that have been excavated with cultural layers dating back to the Ly dynasty (Tống, 2020, pp 169e225), as well as regional-scale contemporary geomorphological data Collineation measurement: a general method for establishing the orientation in the Sinophere countries 2.2 Methodology In ancient China’s urban planning and construction practice, especially in capital cities, the spatial layout and axis systems were closely related to natural and cultural factors This theoretical perspective is usually interpreted at two levels: (1) At the astronomical level, the spatial pattern of the palace cities simulates the symbolic and typical astronomical phenomena, such as the cases of the Mausoleum of Qin Shihuang, Qin Xianyang, Han Chang’an, and Yuan Dadu (Guo, 2019, pp 92e103; Xu, 2019a, p 25) (2) At the geographical level, the city axis system embodies the natural environment’s characteristics From the Qin to the Yuan dynasties, Chinese emperors and planners used collineation measurement to determine the spatial orientation of the capital space (Guo, 2019, pp 68e72; Wu et al., 2019, p 115, pp 132e216) Moreover, scholars of architecture and urban planning considered the collineation measurement as a tradition of ancient Chinese urban planning After examining 1400 ancient Chinese cities, Wang Shusheng (2019) proposed the ’Siwang’, a human-centered approach to the environmental observation that focuses on city-landscape interaction It could provide the foundation for designing the urban pattern and site selection for important buildings Based on 3940 local gazetteers from the Tang Dynasty to the Republic of China, Xu Bin (2019b) confirmed collineation measurement as a technical method to determine the orientation of urban axes and arrange the landscape order in ancient China The above findings and theoretical framework provide the foundation for this research In light of the experience of human settlements in East Asia, this paper examines the design and construction process of the spatial orientation of the Imperial City of Thang Long and its design concept of integrating with nature This paper uses a mixed-method of historical archives, fieldwork, and simulation models First, it introduces the theory and application of collineation measurement, several practice cases in the 11th-13th centuries Second, it uses hypothesis testing with empirical evidence to address the research issue, which entails two research steps: (1) The statistical analysis is used to examine the orientation of the Imperial Citadel of Thang Long using historical archives to create a hypothetical description; (2) The evidence verification is to evaluate the feasibility of the hypothetical description by creating a simulation model on the As per the history of the 11e13th century in Sinosphere countries, collineation measurement is a general method of establishing the orientation of buildings It is a three-point one-line measuring method unique among linear measurement techniques The planner draws on the natural coordinates and combines the artificial coordinates to establish the plane, size, and orientation system of projects on the city scale Mountain peaks, valleys, and huge trees are among the natural coordinates; and wooden poles, stacked stones, and other high-ceilinged structures such as pavilions, towers, and gate houses serve as artificial coordinates The book Ten Computational Canons details the theory and application of this technique Question: Now for (the purpose of) looking at a sea island, erect two poles of the same height, zhang (on the ground), the distance between the front and rear (poles) being a thousand bu Assume that the rear and front poles are aligned (with the island) By moving away 123 bu from the rear pole and observing the island’s peak from ground level, it is noticed that the tip of the front pole coincides with the peak Then by moving backward 127 bu from the rear pole and observing the island’s peak from ground level again, the tip of the back pole also coincides with the peak What is the height of the island, and how far is it from the pole? Answer: The height of the island is li 55 bu; it is 120 li 150 bu from the pole.15 This text is the opening chapter in the book Ten Computational Canons, describing the most straightforward and primary method of using collineation measurement The human observer, the top of the pole, and the mountain peak form a three-point one-line measurement The Chinese in the Eastern Han Dynasty established these two lines of measurement, combined with the triangulation technique and inferred data, such as the proximity and elevation of the relevant terrain (Fig 2) There are many cases applying the method of collineation measurement in practice Albeit limited, this paper explain two examples from the 11the13th century period to illustrate the application and ideology The sacred tree 14 Based on the contents of the city, the mountains, the rivers, the geo-potential and landform in the books of Atlas of Hongduc, Dai Nam’s comprehensive encyclopaedia and descriptive geography of the Emperor Ðồng Kha ´nh 15 ‘有望海岛, 立两表, 齐高3丈, 前后相去1000步, 令后表与前表参相 直。从前表却行123步, 人目著地取望岛峯, 与表末参合。从后表却行 127步, 人目著地取望岛峯, 亦与表末参合。问岛高及去表各几何？答 曰:岛高4里55步;去表102里150步.’see, Se and Swetz 1986, p 105 + MODEL Frontiers of Architectural Research xxx (xxxx) xxx of the mountains and rivers by investigating the surrounding mountains’ location, shape, and cultural connotations, thus creating a great harmony of ’heaven-earth-city-human’ (Wu et al., 2018, pp 68e71) In another instance, the designers of Qiyin Temple in Mentougou, Beijing (the 1100s), surveyed the mountain from the north to south and selected the summits as placement sites The placement and orientation of Qiyin Temple’s structure were built based on the linkage of these two positioning points Finally, the project obtained a mountain view in front and behind, a pagoda for Buddhist relics was added to the placement in the north, on the Jiji Peak This case is a decentralized plan that seeks to unite the temple with the surrounding peaks Based on GIS date (Wu et al., 2018, p 69), further analysis of the positional relationships among the elements effortlessly reveals a three-point measuring line, whose three points include (1) the Buddha’s relic pagoda residing on the Jiji Peak; (2) Qiyin Temple; and (3) the Bijia Peak located at the southernmost point of the overall pattern (see Fig 4) The stele of reconstruction of Qiyin Temple in Yangshan has a detailed record of these dialectical relationships: The peak on the north side is called Jiji Peak, and the name comes from the fact that it is very high and steep and has a Buddha relic pagoda on the top Bijia Peak lies directly south of the lake beyond the temple The temple entrance was constructed to face the southern Bijia Peak, serving as a placement point throughout the construction Three spikes seem to be lined up from the south to the north when viewed from above 17 Fig Survey of a sea island Source: https://en.wikipedia org/wiki/Haidao_Suanjing The above two cases reveal that the collineation measurement approach, in terms of practical application, could be divided into two main types: one is for determining the orientation of the imperial palace, and the other is for shaping the landscape What they have in common is the designer’s observation and thinking about the natural landscape in the creation of artificial buildings, thus establishing a harmonious relationship between ’naturehuman-city (building)’ It could be regarded as the philosophical foundation of ancient urban planning and design in the Sinosphere countries was assigned to the south and used as a placement point to define the forbidden city’s centreline while building the capital city Yuan Dadu in 1266 by the planner Liu Bingzhong (Wu et al., 2018, pp 68e70) The ancient book, Chronicles of Capital City Dadu in the Yuan Dynasty (Xijinzhi Jiyi), which Xiong Mengxiang compiled, recorded that Liu Bingzhong determined the orientation of the imperial palace of Yuan Dadu: When Kublai Khan was constructing the Yuan Dynasty’s capital, he sought counsel from Liu Bingzhong, a Grand Guardian, on the city’s orientation The emperor consented, calling the tree The Sacred Tree and awarding it a gold medal as a reference point and benchmark Liu Bingzhong responded that he would use a tree south of the third bridge outside the Lizheng Gate as a reference point, and the emperor agreed.16 Historical backgrounds of the Imperial Citadel of Thang Long 4.1 Construction of the Imperial Citadel of Thang Long The construction of the Imperial Citadel of Thang Long took place during the regime change in Vietnam Le ˆ Long Ð~ınh, `n Le ^ˆ the last emperor of Tie ˆ dynasty, died on 20 November 1009, in the capital city of Hoa Lư.18 Ly ˆng Uẩn ´ Co (974e1028), an emperor with military strength, took over In addition to the large trees in the south, Liu Bingzhong used the Yangshan Mountain peak as the coordinate point at an angle of 60 from the central axis and used the Niutiling peak as the coordinate point along the central axis (Fig 3) In this process, the planner placed the capital in the order 17 ‘北曰级级峰, 言高峻也, 有佛舍利塔在其绝顶.水外正南为笔架 峰, 自寺望之, 屹然三尖, 与寺门对, 出乎层青迭碧之表 ’ see Wu et al., 2018, p 69 18 Hoa Lư is a district of Ninh Bı`nh Province in the Hồng River Delta region of Vietnam Before 1010, Hoa Lư served as the capital of Ðại Cồ Việt 16 ‘世皇建都之时, 问于刘太保秉忠, 定大内方向。秉忠以丽正门外 第三桥南一树为向以对, 上制可, 遂封为“独树将军”, 赐以金牌.’ Xiong Mengxiang, Xilu Zhi Jiyi析津志辑佚 [Chronicles of Capital City Dadu in the Yuan Dynasty] (Beijing: Beijing Guji Chuban She, 1983), p 213 see Xiong, 1983, p 213 + MODEL T Dinh and X Ren Fig The landscape order of Dadu, Source: Wu et al., p 70 the early construction phases, the rulers temporarily used the remaining palaces and infrastructure of Ðại La while building the new capital (Bu `i and Tống, 2010, pp 27e31) The Imperial Citadel of Thang Long was roughly built in three phases: (1) survey and site selection, which took place from the winter of 1009 to the spring of 1010; (2) implementation, which was accomplished during the early winter of 1010 to the late winter of 1017 and included the completion of palace projects for the administration and service of the emperor as well as the construction of the city wall; and (3) construction of the residential area from 1017 to 1030 (Phạm, 2013, pp 91e94; Momoki, 2010, p 2) Royal chronicles detailed the site selection, planning, and construction of Thang Long city: 1010, Feb Furthermore, Dai La citadel, the ancient citadel of lord Gao Pian, is situated in the space between Heaven and Earth, where the dragon is coiled and the tiger crouching The capital is laid out on North-South East-West axes and is favourably situated concerning the mountains and river The site is large and flat, the fields high and well enough exposed The population is protected against high water and floods Everything there flourishes and prospers It is a beautiful site where men and riches from the four cardinal points converge.20 Fig The collineation lines of Qinyin Temple Source: Wu et al., p 69 ng Long Imperial City, Trie ^` 1010 in the Tha ˆu Nguyễn  ` ^ palace was built, Tập Hieˆn was built on its left, Giảng Vo ˜ was built on its right Phi Long Gate was open on the left, Ðan Phượng Gate was open on the right In the middle area of the south, Cao Palace was built with a terrace `u Nguyễn palace, Long An ^ˆ called Long Trı` behind the Trie and Long Thụy were built Nhật Quang was built on right and Nguyệt Minh was built on its left, Thu ´y Hoa was built behind Four gates were opened on the four sides of the city: Tường Phu ` on the east, Quảng Phu ´c on the west, Ðại Hưng on the south, and Diệu Ðức on the north Hưng and established the Ly ´i Tổ (Le ˆ ´ dynasty, known as Ly ´ Tha et al., 1998, p 109) Wary of the previous dynasty’s residual influence, Ly ´i Tổ chose to relocate the capital of ´ Tha Ðại Việt to the site of the Ðại La Citadel, which is now modern Hanoi, in March 1010.19 The emperor and his court completed the relocation of the capital and changed the name of Ðại La to Thang Long in August and September of the same year, respectively (Le ˆ et al., 1998, p 110) During 19 Ðại La was the southernmost province of China in Tang Dynasty from 679 to 866 Jiedushi Gao Pian constructed Ðại La in 866 It was the seat of Tống Bı`nh County during the Tang dynasty, and was the capital of the T~ınh Hải qua ˆn Ðại La was favoured because of its central and convenient location, defensible terrain, and relatively dry climate 20 ‘况髙王故都大羅城, 宅天地區域之中, 得龍蟠虎踞之勢, 正南北東 西之位, 便江山向背之宜 其地廣而坦平, 厥土髙而爽塏 (音愷, 髙燥 也), 民居蔑昏墊之困, 萬物極蕃阜之豐 遍覽越邦, 斯為勝地 誠四方 輻輳之要會.’ see Le ˆ et al., 1998, p 109 + MODEL Frontiers of Architectural Research xxx (xxxx) xxx Fig The urban structure of the capital city of Thang Long in the Ly ˆ, 1490, p 172 ´ dynasty Source: Le wall divided the city space into three functional areasdthe Imperial Citadel, the Royal City, and the Capital City The Imperial Citadel was located in the northern part of the walled city and had a rectangular structure with Nu `ng Mountain at its centre and the emperors residence on top of it The four city walls surrounding the Imperial Citadel are 770m long (Phan, 2010a, p 46) Although the emperor’s residence was rebuilt several times, its position and orientation remained unchanged At present, only the base of the emperor’s residence remains, which is the site of Kı´nh Thie ˆn Palace The Royal City, located west of the Imperial Citadel and south of West Lake, was where the royal army drilled, hunted, and relaxed The Royal City surrounds the Forbidden City, and is a rectangular plan with short east-west sides and long northsouth sides, maintained by the city walls The eastern wall of the Imperial City was located at the present-day ´ ~, 1966, p 42), the northern wall Thuốc Ba ˘c (Trần and Vu of the Imperial City was located at Phan Ðı`nh Phu `ng), the western wall was located at present-day Ngọc Ha `, and the southern wall crossed present-day Lenin Square (Tống, 2020, p 172) The highest topographical location was the mountain of Kha ´n, the commanding platform for troop exercises and is now the site of the Presidential Palace, in the Royal City The Capital City, situated in the southern part, was the living space for the residents ~ Phụng Observatory were built in Thie ˆn Temple and Ngu ´ng Nghie ˘ the city, and Tha ˆm Temple was built on the south side of the city.21 The two paragraphs above reveal that the site selection of Thang Long city took into consideration geo-potential and landform, and safety, production, transportation, and landscape aesthetics The logic of the site selection is similar to that of Sui and Tang Dynasties’ capitals Chang’an (Now  (now Kyoto) in Japan The Xi’an) in China and Heian-kyo planning and design method begins in the middle and progresses from left to right and front to rear This method reflects a clear notion of overall orientation by overlapping the geographical order with the ritual order 4.2 Urban from and structure Phan Huy Le ˆ (2010a, p 21), Tống Trung Tı´n (2020, pp 172e3), and Nguyễn Quang Ngọc (2010, p 97) recovered the plan of the capital city of Thang Long (Fig 5) Thang Long was located in the districts of Ba Ðı`nh, Hoa `n Kiếm, Ðống Ða, and Hai Ba ` Trưng of modern Hanoi The city 21 ‘昇龍京內起朝元殿, 左置集賢殿, 右置講武殿, 左起飛龍門, 右起 丹鳳門。正陽啟髙殿階曰龍墀。墀內翼以逥廊周匝四面。朝元殿後置 龍安龍瑞二殿。左鍵日光殿, 右鍵月明殿。後有翠花宮。城之四面啟 四門。東曰祥符, 西曰廣福, 南曰大興, 北曰耀德。又於城內起興天 寺、五鳳星樓。離方創勝嚴寺 ’ in Anonymous, 1300s Việt Sử Lược [The concise summary of the Vietnamese historical records] reproduced in the online version of the Siku Quanshu in the Kanseki Repository, Kyoto University’s online database of premodern Chinese texts http://www.kanripo.org/text/KR2i0023/002#1a,pp 002-3b, 002-4a 4.3 A 9 deviation of orientation system It is important to stress that the ruler of the Ly ´ Dynasty abandoned the former orientation system of the Ðại La Citadel and created a new one for the capital city + MODEL T Dinh and X Ren the Trần Dynasty, who usurped the throne from the Ly royal family Unable to deal with the regime transition, he left Thang Long city and lived in seclusion in Ye ˆn Tử Mountain Trần Thủ Ðộ, as the imperial master, planned a new palace city in Ye ˆn Tử Mountain district The central axis of the royal city’s design was the line from Thie ˆn An Palace to Ðoạn Minh Palace, and biaojueshanzhong (meaning collineating the peak of Tuyet Mountain) was the essential technique for establishing the axis orientation as documented Mountain and river landscapes are shaped in part by the method of collineation measurement, which is useful for establishing orientation and creating the landscape The historical elements of Vietnamese poetry provide the exemplifications, such as ’the spacious fields stretched out in front of the mausoleum feud, and the tiered peaks of the mountain facing the capital’s gates’ (Ða `o et al., 1978, p 143) According to archaeological evidence, the Ðại La Citadel is located under the ruins of the Imperial Citadel of Thang Long and has its orientation system (along an azimuth of 176 ) (Tống and Bu `i, 2010, pp 42e3) The orientations of the two cities have a 9 deviation Assuredly, changing the orientation system posed a great challenge to the project In most cases, if a ruler wanted to construct a new citadel on top of the foundations of an existing one, the most costeffective and practical option would be to utilize the base for expansion or creation; because of the new spatial orientation, there were no amenities at the time that could be used Presumably done deliberately for the rulers of the Ly ´ Dynasty, designing the new orientation and layout was of great political significance Statistical analysis: historical clues and design perspectives related to the spatial orientation 5.2 Three design perspectives related to the natural landscape 5.1 Historical clues related to the collineation measurement Royal geographical and historical materials indicate a dialectical relationship between the orientation of the Imperial Citadel and the surrounding mountains The results of clue statistics reveal three essential design perspectives related to orientation issues:(1) the highland, (2) the central mountains, and (3) the Hall of Brightness The materials from the 11th to 13th centuries, record the construction or renovation of the palace city, provide a comprehensive understanding of the planning process in Vietnam during that period Both Concise summary and Complete book point out that the method of collineation measurement22 was applied to determine the orientation of Imperial Citadel in the Ly Dynasty of Vietnam The following are two historical texts: 5.2.1 The highland The highland involves the location of Tản Vie ˆn Mountain, Nu `ng Mountain, and the Imperial Citadel of Thang Long It refers to a lengthy stretch of highland that runs from west to east on a regional scale Following are some of the most important historical documents: In July 1071, [the craftsmen] established artificial coordinates (libiao) to build five buildings, including the Trường Quảng Gate, Tha ´i Bı`nh Gate, Thủy Ha ` Thượng Gate, Nghe ˆnh Thu Shrine and Quy Nha ˆn Post.23 This is the land where the Dragon Vein is, reaching from the mountain of Tản Vie ˆn, and ending at the River of Hồng.25 In January 1237, Hence, [Thu Do] collineated the peak of Tuyet Mountain(biaojueshanzhong), designed here would be Thie ˆn An palace, there would be Ðoạn Minh tower, ordered the craftsmen to build it 24 In the past, Hanoi was the town of Thang Long Geomantic principles define this stretch of land as reaching from Tản Vie ˆn Mountain in the province of Sơn Ta ˆy From there, it follows the winding course of the Ha ´t River before crossing it and ending at Nu `ng Mountain The main building of the emperor’s residence is located on Nu `ng Mountain.26 The Chinese terms libiao and biaojueshanzhong are important evidence in the above-mentioned historical sources In 1072, during an enlargement project of Imperial Citadel of Thang Long, the first task was libiao (meaning the establishment of artificial coordinates) Additionally, the second text in 1237 described a plan that failed to be implemented by Trần Tha ´i To ˆng (1218e1277), the first monarch of These two descriptions suggest a highland originating from Tản Vie ˆn Mountain, extending eastward and ending at Nu `ng Mountain The location of the Imperial Citadel of Thang Long appears to be closely related to this highland (Fig 6) This highland is a natural feature in historical, poetic writings, forming a binary antithesis to the Hồng river (meaning The Red River) The mountains are associated with dryness and safety, and the Hồng river with wetness and fertility In addition, from the perspective of waterway transportation, the highland was an isolated island on a large swamp, resulting in a beautiful landscape 22 Collineation measurement was one of the construction techniques of the 11th-13th centuries in the Sinosphere countries For details of the Zhongdu of the Jin Dynasty (1151) and Dadu of the Yuan Dynasty (1267), see Wu et al., 2018 23 ‘立表造長廣門、太平門、上水河門、迎秋祠、歸仁驛凡五處.’ in Anonymous, 1300s Việt Sử Lược [The concise summary of the Vietnamese historical records] reproduced in the online version of the Siku Quanshu in the Kanseki Repository, Kyoto University’s online database of premodern Chinese texts http://www.kanripo.org/text/KR2i0023/002#1a, p 002-22a 24 ‘守度再三固請, 未蒙俞允, 乃謂眾曰:「凣乘興所在, 即是朝廷」 遂表蕝山中, 此處天安殿, 彼處端明閣, 差人營造 ’see Le ˆ et al., 1998, p 172 25 ‘抑彼龙状形胜斯在。伞圆是维。富良 (红河) 为带 ’see Nguyễn, 1882, p 29 26 ‘河內舊升隆城也.傘圓山出脈, 渡喝江 (今底江) 迢遞而來, 至農 山而止。今為行宮正殿.’see Ngo ˆ et al., 2004, p 1450 + MODEL Frontiers of Architectural Research xxx (xxxx) xxx Fig The axis or ‘highland’ of the Imperial Citadel of Thang Long Source: Self-painted by author effect This content may be found in a poem written by Vietnamese poets, such as ’In the early morning, following the Nhi river (the Hồng river) as it flows eastwards, [I] look back and see the Tan Linh Mountain and Nung Son, which are faintly visible in the clouds’27 and ’ Tản Vie ˆn Mountain has been famous from ancient times, looking from the city into the distance in a mass that looks like round umbrellas’.28 Fig The centre of the Imperial Citadel of Thang Long Source: Self-painted by author 5.2.2 The central mountains The second is on the central mountains, involving Nu `ng Mountain, Tam Mountain, Khan Mountain, and the emperor’s Palace The books of Descriptive Geography of Việt Kingdom and Complete Atlas of the Ðại Việt Kingdom indicate that Nu `ng Mountain was placed at the centre of the Imperial Citadel: The mountain of Nu `ng is located in the centre of the city When the Ly ´ Dynasty set the capital, Nu `ng Mountain was used as the foundation of the Emperor’s residence, where the palace of Kı´nh Thie ˆn is located The mountain of Tam is located on the north side of Nu `ng Mountain in the Thang Long city and is the pillow of Nu `ng Mountain.29 The base of the palace of the Kı´nh Thie ˆn is a flat plateau protruding from the level ground The mountain of Nu `ng is located in the middle, where the palace is located, and behind it is Tam Mountain, with Khan Mountain on the right 30 Fig The Brightland of the Imperial Citadel of Thang Long Source: Self-painted by author These indicate that Nu `ng Mountain was the base of the emperor’s residence and the centre of the Imperial Citadel Tam Mountain, behind (north) Nu `ng Mountain, is likened to the pillows of the Imperial Citadel On the right (west) of Nu `ng Mountain, Khan Mountain is recognized as the viewing platform of the citadel In the dialectical whole of the three, the existence of Tam Mountain and Khan Mountain is to emphasize the central consciousness of Nu `ng Mountain and the Imperial Citadel (Fig 7) 5.2.3 The Hall of Brightness The third is the viewpoint of the Hall of Brightness (Mingtang in Chinese), which connects the region that can directly be seen along with the mountains of Ðội and Ðiệt from the emperor’s residence The following passage describes the view from the emperor’s residence: a hinterland with visible sunrise and sunsets, runoff from three rivers, and vast landscapes (Fig 8) 27 ‘珥河詰旦東回首, 傘嶺濃山隱約間 ’see Ðinh et al., 1998, p 106 28 ’名山山上古今传, 四望团团若伞圜 ’see Cao, 1976, p 190 29 ‘農山在城正中。李朝定都以斯山為正殿台迨。黎朝為敬天殿。今 奉建為皇宮前殿”、“三山在成內農山之北。古傅此山為農山正殿之 枕 ’see Le ˆ 1833, p 18 30 ‘敬天殿基乃平地土阜突出高平方正。地鉗記云農山居中正即此, 其後催出為三山, 其右催出為看山.’see Nguyễn, 1900, p 22 Facing south from [the Emperor’s residence], [one] could see the mountains of Ðội and Ðiệt The impetuous To ˆ Lịch River runs past on the right, and the Nhuệ, Ngưu, and To ˆ Rivers embrace the town in front Their currents meet at the Luong confluence and empty into the Hồng + MODEL T Dinh and X Ren Fig Distribution and geographic information of mountains around the Imperial Citadel of Thang Long Source: Self-painted by author 105.97426 E), south of modern Hanoi City and 52 km from Nu `ng Mountain (Fig 9).32 In sunny weather, people can see the scenery of Tản Vie ˆn Mountain when looking west from the relics of the Imperial Citadel of Thang Long (Fig 10) River before flowing down to Hưng Ye ˆn, Nam Ðịnh, and the sea These areas are the Hall of Brightness of the Ha ` Nội region.31 Evidence verification: interpreting the design logic of the orientation system 6.2 The identification of the highland By importing the information about the city walls and mountains listed above into GIS, this paper recovers and locates them using geographical data from the Atlas of Hongduc and The Descriptive Geography of the Emperor Dong Khanh (Ngo ˆ et al., 2004, pp 5e22; Le ˆ,1490, pp 5e6) This section uses the following four steps to verify the three perspectives mentioned above (part 5.2) The highland of the Imperial Citadel of Thang Long was a long, bar-shaped geological vein that originated from Tản Vie ˆn Mountain and stretched from west to east It can be regarded as a rare natural dike located in the Hồng river basin that provided a habitat close to the mainstream without fearing flood The archaeological and geological data (Bu `i and Nguyễn, 2015; Tống, 2020), imported into the GIS platform, reveal a dependency between the location of the Imperial Citadel and the highland Nu `ng Mountain is a highland rising from its proximity to the Hồng river The Imperial Citadel and Royal City were located above the highland, and the Royal City had a long east-west and narrow north-south pattern (Fig 11) The northern wall of the capital city also spreads in the direction of its elongation 6.1 The geographic positioning of mountain peaks Nu `ng Mountain was located under the site of Kı´nh Thie ˆn Palace (21.03662 N, 105.84027 E) Tam Mountain was located north of Nu `ng Mountain and east of the North Gate of the modern Hanoi Citadel (21.04069 N, 105.84189 E) Kha ´n Mountain was east of Nu `ng Mountain and at the entrance of the modern Presidential Palace (21.03929 N, 105.83449 E) Tản Vie ˆn Mountain was located at the Ba Vı` National Park (21.06979 N, 105.35641 E), west of modern Hanoi city and 50 km away from Nu `ng Mountain The two peaks of Long Ðội Mountain were Ðội Mountain and Ðiệp Mountain, located in Duy Tie ˆn County, Ha ` Nam Province (20.58529 N, 6.3 The identification of the central mountains Historical sources emphasize that Nu `ng Mountain was the center of the Imperial Citadel Nevertheless, geographic information analysis provides comprehensive visual data on its layout The ground surrounding Nu `ng mountain displays numerous slope hillocks with a west-east tendency, with a hillock in each of the four directions of the mountain, influenced by the stratigraphic structure The northern 31 ‘正殿南向, 前峙队、迭二山, 后枕三山。珥河遶其左。 苏历 为悍气流过右边, 与鋭江、牛江、苏江濴迴其前, 同注于良三岐, 出珥 河 上福、富川、维先、金榜等县地势卑湿水淤田多夏務, 为河内 局之明堂水.’ see Ngo ˆ et al., 2004, pp 1450e1 32 The positioning data in this paper are based on the geocentric coordinate system and IERS Reference Meridian coordinate system 10 + MODEL Frontiers of Architectural Research xxx (xxxx) xxx Fig 10 The actual image of Tản Vie ˆn Mountain The distant view is of the Tản Vie ˆn mountain, the closer view is that of Hanoi city, and the closest is that of the Hồng river Source: Photographed by author hillock rises from Tam Mountain; the western hillock rises from Kha ´n Mountain; and the eastern and southern hillocks have broad, apparent shapes The east, north, and west city walls of the palace, as well as the northeast, northwest, and southwest corners of the Royal City, were built on these sloping hillocks, according to archaeological evidence (Phan, 2010a, p 21; Tống, 2020, pp 169e225) (Fig 12) 6.4 The identification of the Hall of Brightness Furthermore, the Hall of Brightness of the Imperial Citadel was only ideal in historical landscape texts, most likely poetic imagery of the natural environment The positional relationship between the emperor’s residence and the three mountains of Ðội, Ðiệp, and Tam was only Fig 11 Overlay analysis map of geological and archaeological information of the Imperial Citadel of Thang Long Source: Selfpainted by author 11 + MODEL T Dinh and X Ren Fig 12 Overlay analysis map of topographical and archaeological information around the Imperial Citadel of Thang Long Source: Self-painted by author Fig 13 Archaeological map of the western part of the Imperial Citadel of Thang Long, adapted from the Institute of Imperial Citadel Studies, Vietnam 12 + MODEL Frontiers of Architectural Research xxx (xxxx) xxx 275 (Tống, 2020, p 205) (Fig 13) Coincidentally, the mountain of Tản Vie ˆn is located in this direction, 50 km from the site relative It is likely a poetic and symbolic record of the natural environment by the ancients Thus, the principal factor that influenced the orientation of the Imperial Citadel was not the Fengshui concept of the Hall of Brightness but rather the underlying stratigraphy Whether it was site selection, designation of a centre, delineation of boundaries, or planned expansion of space, the decision seemed to concern the highland that ran from the mountains of Tản Vie ˆn and Nu `ng Definitively, this highland is the key to identify the geography By analysing the archaeological excavation data, the study identifies another possibility for understanding the orientation system, namely that the palace orientation could be along an azimuth of 185 or 275 at the same time Archaeological data confirm that the western part of the Imperial Citadel site contains a group of high-level palaces and a road for the imperial carriage, along an azimuth of The application of technique in designing the spatial orientation of Imperial Citadel of Thang Long Through fieldwork and observation, ancient designers could roughly extrapolate the morphology, extension, and direction of the geographical situation of their surroundings However, the use of natural elements in construction must be standardised, which relies on collineation measurement There are two technical forms of collineation measurement known so far: (1) seeking natural orientation along or on an azimuth parallel to the central axis; (2) rarely, seeking natural orientation on an azimuth at an angle of 60 from the Fig 14 Simulation line of collineating two peaks of the mountains to the west of the Imperial Citadel of Thang Long Source: Self-painted by author 13 + MODEL T Dinh and X Ren central axis in the case of Jiankang, the capital city in the Six Dynasties (220e589 CE) While in the case of Imperial Citadel of Thang Long, its approach to the orientation is to seek natural orientation in the direction perpendicular to the central axis, that is, in the azimuth of measuring the Tản Vie ˆn Mountain Such an orientation design approach can be considered an innovative mode in designing the orientation, built on natural geography We used GIS and LIM to conduct a computer simulation of collineation measurement to test the possibility (azimuth of 275 ) When the line of collineation measurement was set at an azimuth of 275 , an integral line was formed between the south city wall of the Imperial Citadel, the northern peak of Tản Vie ˆn Mountain (21.06979 N,  ´ 105.35641 E), and the peak of Tha ˘ng Mountain (21.0964 N, 105.19959 E) The simulation results indicate that this line of collineation served as a reference base for both the construction of the Imperial Citadel and the Royal City In addition, the line extended to the east and stretched to the Isle of Jade Islet (the site of the modern Temple of Jade Mountain) and the Mountain of Ðộc To ˆn (modern Pen Tower; 21.0306 N, 105.85337 E) Presumably, the Mountain of Ðộc To ˆn, the northern peak of Tản Vie ˆn Mountain, ´ng Mountain were the base coordinates ˘ and the peak of Tha of the line of the collineation measurement (Fig 14) Based on the logic and application, this technique is referred to as the ’collineating Two Mountain peaks to the West’ The Ly ´ Dynasty built many high-grade religious buildings on this line of collineation measurement Historical remains of these buildings still existed, such as the Temple of Tản Vie ˆn Mountain, the Temple of Jade Mountain, and the Temple of Ðộc To ˆn Mountain In terms of political symbols, Tản Vie ˆn Mountain is the national mountain of Vietnam Many politicians consider the highlands from Tản Vie ˆn Mountain to Nu `ng Mountain to be the country’s foundation As the Complete book recorded, Conclusions In summary, the keyword for designing the orientation of the Imperial Citadel of Thang Long is harmony, which is an essential concept in the wisdom of traditional Eastern city construction The city is an extension of the mountains, and the mountains are also a spatial component of the city The structure from the mountain to the city provides the foundation for the living environment, and the natural sequences from the city to the mountains constitute the city’s landscape order The setting of the orientation system of the Imperial Citadel of Thang Long was far beyond the scope of the city In essence, the collineation measurement is a regional planning technique corresponding to 50 km to arrange a sustainable habitat and establish an urban space and landscape structure However, this construction concept emerged in the 11th century but was quite advanced, whose scope is close, if not identical, to the planning area outlined in the Hanoi Master Plan (2010), which includes territorial spatial planning As Joseph (2004, p 91) argued, the Sinosphere thinkers sought order and harmony throughout natural phenomena and considered this ideal in all human relationships Many ancient capital cities in Vietnam, such as Hoa lư, Ta ˆy Ðo ˆ, Lam Kinh and Huế, all have a dialectical connection with the surrounding mountains As an essential branch of traditional oriental urbanism, Vietnamese capitals are artificial nature within holistic nature Thus, identifying the mountain-city relationship helps to understand the theory of sciences of human settlements and allows for a deeper understanding of built heritage’s human and intangible values Furthermore, from the perspective of cultural transmission, the design of Thang Long City is in line with the techniques and methods of ancient Chinese capitals and can be considered an innovative product in the process of technology diffusion in the Sinosphere The Imperial Citadel of Thang Long serves as a significant case study for comprehending the inclusivity of ancient East Asian culture and inspires more profound thoughts about the general and specific principles of East Asian heritage Surrounded by Tan Vien mountain and the Lo Nhi river (means the Hồng river), Long Do (means Hanoi) has high mountains and deep waters, flat and extensive land Since ancient times, when emperors built their foundations and states, they always chose this place as their capital, believing it to be a solid and unshakable foundation.33 Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Additional, a popular folk song indicates a close relationship in belief and culture between Tản Vie ˆn Mountain and Ðộc To ˆn Mountain, e.g ‘the first plateau is Tản Vie ˆn Mountain, the third one is Tam Ðảo Mountain, and the second one is Ðộc To ˆn Mountain’ (Ðoa `n, 2010, p 246) Ancient Vietnamese designers identified and observed the surrounding mountains and tried to standardize the elements of the natural environment and integrate them into the construction of the artificial city By collimating the two mountain peaks to the west, they set the baseline for positioning, based on which they determined the location and spatial orientation of the Imperial Citadel Acknowledgements We thank Mr Vo ˜ Ðı`nh Ðo ˆng Nghi, whose research on the ancient geography and feng shui of Vietnam, for generously giving his time to assist with the 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Capital City The Imperial Citadel was located in the northern part of the walled city and had a rectangular... of the imperial palace, and the other is for shaping the landscape What they have in common is the designer’s observation and thinking about the natural landscape in the creation of artificial