Constantinople. Krum doubled the country's territory, killed Byzantine emperor Nicephorus I in the Battle of Pliska, and introduced the first written code of law. Then in 864 Boris I abolished paganism in favour of Eastern Orthodox Christianity. The Cyrillic Alphabet was created in Bulgaria's capital Preslav, becoming the official alphabet of Bulgaria in late IX century AD. Shortly after the Cyrillic Alphabet started its gradual spread from Bulgaria to Slavic nations to the north and north east of Bulgaria. Simeon the Great's 34-year rule began in 893 and saw the largest territorial expansion of Bulgaria, along with a golden age of Bulgarian culture.
Wars with Croatians, Magyars, Pechenegs and Serbs and the spread of the Bogomil heresy weakened Bulgaria after Simeon's death. Two consecutive Rus' and Byzantine invasions resulted in the seizure of the capital Preslav by the Byzantine army in 971. Under Samuil, Bulgaria somewhat recovered from these attacks and managed to conquer Serbia and Albania, but this rise ended when Byzantine emperor Basil II defeated the Bulgarian army at Klyuch in 1014. Samuil died shortly after the battle, and by 1018 the Byzantines had ended the First Bulgarian Empire.
Second Bulgarian Empire
After his conquest of Bulgaria, Basil II prevented revolts and discontent by retaining the rule of the local nobility and recognising the autocephaly of the Archbishopric of Ohrid. After his death Byzantine domestic policies changed and a series of unsuccessful rebellions broke out, the largest being led by Peter Delyan. In 1185 Asen dynasty nobles Ivan Asen I and Peter IV organised a major uprising which resulted in the re-establishment of the Bulgarian state. Ivan Asen and Peter laid the foundations of the Second Bulgarian Empire with Tarnovo as a capital.
Kaloyan, the third of the Asen monarchs, extended his dominion to Belgrade and Ohrid. He acknowledged the spiritual supremacy of the Pope and received a royal
