Bulgarian Empire also intervened in the internal affairs of Byzantium Tervel sheltered the exiled Emperor Justinian II and assisted him to regain his throne in Constantinople in 704 In 716 Tervel forced a treaty on Byzantium, which awarded northern Thrace to Bulgaria and reiterated Constantinople’s annual tribute Because of this treaty, Tervel came to the aid of Byzantium during the Arab siege of the town in 717, crucial to averting the fall of Constantinople Tervel’s attack surprised the Arab forces, and many of them were slaughtered (some count 100,000) After Tervel’s death the remainder of the eighth century was a time of internal strife, until the rule of Khan Kardam (777– 802) Kardam inflicted a number of severe defeats on the Byzantine army and in 796 forced Constantinople to renew its annual tribute to Bulgaria It was Kardam’s successor Khan Krum (803–814) who achieved one of the greatest expanses of the First Bulgarian Empire Krum is believed to have spent his youth establishing his authority over large swaths of modern-day Hungary and Transylvania When he became khan, Krum added these territories to Bulgaria Thus his realm stretched from Thrace to the northern Carpathians and from the lower Sava River to the Dniester, and bordered the Frankish Empire of Charlemagne along the river Tisza Krum’s expansionist policy brought him into conflict with Byzantium In 809 he sacked the newly fortified town of Serdica (present-day Sofia) and surged into the territory of Macedonia The imperial army destroyed the Bulgarian capital at Pliska Krum, however, besieged the Byzantine troops in a mountain pass, where most of them were massacred Emperor Nikephoros I lost his life, and Krum ordered that Nikephoros’s skull be encrusted in silver and used it as a drinking cup After his military success Krum unleashed a total war against Byzantium, laying waste to most of its territory outside the protected walls of Constantinople He died unexpectedly in 814 in the midst of preparations for an attack on the metropolis The emphasis on Krum’s military prowess often neglects his prescience as state-builder He was the first Bulgarian ruler that began centralizing his empire by providing a common administrative and legal framework His son Khan Omurtag (r 814–831) followed his father in further consolidating the state Omurtag’s main achievement was to improve the legal system developed by Krum He was also an avid builder of fortresses Under Omurtag’s successors, Malamir (r 831–836) and Pressian (r 836–852), the First Bulgarian Empire penetrated further into Macedonia Their reign, however, saw an increase in the internal crisis of the state 53 because of the spread of Christianity Both the Slavs and the Bulgars practiced paganism, but a large number of the Slavs had begun converting to Christianity However, the Bulgars and especially their boyars (the aristocracy) remained zealously pagan Krum and, in particular, Omurtag became notorious for their persecution of Christians A new era in the history of the First Bulgarian Empire was inaugurated with the accession of Khan Boris (r 852–888) Boris confronted the social tensions within his state as a result of the distinct religious beliefs of the population In 864 he accepted Christianity for himself and his country With this act, Boris increased the cohesion of his people Internationally he also ensured the recognition of his empire, as all the powers of the day were Christian In 888 Boris abdicated and retired to a monastery The throne passed to his eldest son, Vladimir (r 889–893), who immediately abandoned Christianity and reverted to paganism, forcing Boris to come out of his retirement in 893 He removed and blinded Vladimir and installed his second son, Simeon, to the throne The reign of Simeon the Great (893–927) is known as a golden age Simeon extended the boundaries of the Bulgarian Empire west to the Adriatic, south to the Aegean, and northwest to incorporate most of present-day Serbia and Montenegro He besieged Constantinople twice, and Byzantium had to recognize him as basileus (czar, or emperor); the only other ruler to whom Constantinople extended such recognition was the Holy Roman Emperor In order to indicate the break with the pagan past, Simeon moved the Bulgarian capital from Pliska to nearby Preslav In Preslav, Bulgarian art and literature flourished with unprecedented brilliance Despite these exceptional developments, Simeon’s reign was followed by a period of political and social decay His son Petar (927–970) was involved in almost constant warfare; the nobility was engaged in factionalist strife, and the church fell to corruption The general corrosion of the state was reflected by the spread of heresies among the Bulgarians By the end of the 10th century the Bulgarian Empire was in rapid decline In 971 the capital, Preslav, and much of eastern Bulgaria was conquered by Byzantium Under the leadership of Czar Samuil (997–1014), Bulgaria had a momentary resurgence, with the capital moving to Ohrid Under Samuil the country expanded into present-day Albania, Montenegro, and parts of Thrace However, in 1014 Emperor Basil II “Bulgaroktonus” (the Bulgarian-slayer) captured 15,000 Bulgarian troops and blinded 99 out of every 100; the remainder were left with one eye to guide their comrades back to their czar When Samuil