Byzantine–Bulgarian wars: Battle of Kleidion: Byzantine emperor Basil II inflicts a decisive defeat on the Bulgarian army, and his subsequent treatment of 15,000 prisoners reportedly causes Tsar Samuil of Bulgaria to die of a heart attack less than three months later, on October 6.

The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantine Empire and Bulgaria which began after the Bulgars conquered parts of the Balkan peninsula after 680 AD. The Byzantine and First Bulgarian Empire continued to clash over the next century with variable success, until the Bulgarians, led by Krum, inflicted a series of crushing defeats on the Byzantines. After Krum died in 814, his son Omurtag negotiated a thirty-year peace treaty. Simeon I had multiple successful campaigns against the Byzantines during his rule from 893 to 927. His son Peter I negotiated another long-lasting peace treaty. His rule was followed by a period of decline of the Bulgarian state.

The Battle of Kleidion took place on 29 July 1014, between the Byzantine Empire and the Bulgarian Empire. It was the culmination of the nearly half-century struggle between the Byzantine Emperor Basil II and the Bulgarian emperor Samuel in the late 10th and early 11th centuries. The result was a decisive Byzantine victory.

The foundation of Constantinople in 330 AD marks the conventional start of the Eastern Roman Empire, which fell to the Ottoman Empire in 1453 AD. Only the emperors who were recognized as legitimate rulers and exercised sovereign authority are included, to the exclusion of junior co-emperors who never attained the status of sole or senior ruler, as well as of the various usurpers or rebels who claimed the imperial title.

Basil II Porphyrogenitus, nicknamed the Bulgar Slayer, was the senior Byzantine emperor from 976 to 1025. He and his brother Constantine VIII were crowned before their father Romanos II died in 963, but they were too young to rule. The throne thus went to two generals, Nikephoros Phokas and John Tzimiskes before Basil became senior emperor, though his influential great-uncle Basil Lekapenos remained as the de facto ruler until 985. His reign of 49 years and 11 months was the longest of any Roman emperor.