Nikephoros I in the context of "Michael I Rhangabe"

Bulgarian Battle of Versinikia (Bulgarian: Битката при Версиникия; Greek: Μάχη της Βερσινικίας) was a battle fought in 813 AD between the Byzantine Empire and the Bulgarian Empire, near the city of Adrianople (Edirne), in modern-day Turkey.

The Bulgarian army, led by Krum of Bulgaria, defeated the Byzantine forces. Following this defeat, Michael I Rangabe abdicated, with Leo V the Armenian taking the Byzantine throne. The battle further strengthened Bulgarian control in the region after their victory over Nikephoros I two years earlier. After the battle, the Bulgarians controlled the whole region of Eastern Thrace (until the Byzantine–Bulgarian Treaty of 815), with the exception of a few castles that remained in Byzantine control. Krum died on 13 April 814, but his muster of "5,000 iron-plated wagons [ . . . ] to carry the siege equipment" alarmed the Byzantine court to such an effect that they asked for the aid of the Carolingian Emperor Louis the Pious. These large-scale military preparations were Krum's attempt to avenge his failure at the Second Bulgarian Siege of Constantinople one year prior.

Michael I Rangabe (also spelled Rhangabe; Greek: Μιχαὴλ Αʹ Ῥαγκαβές, romanized: Mikhaḗl 1 Rhangkabés; c. 770 – 11 January 844) was Byzantine emperor from 811 to 813. A courtier of Emperor Nikephoros I (r. 802–811), he survived the disastrous campaign against the Bulgars and was preferred as imperial successor over Staurakios (r. 811–811), who was severely injured. He was proclaimed emperor by Patriarch Nicephorus I of Constantinople on 2 October 811.

Michael's policies were generally conciliatory, and he was overwhelmingly influenced by the iconodule clerics Nikephoros and Theodore the Stoudite. He improved relations with the Franks, even to the point of recognising Charlemagne as an emperor – although not "of the Romans" – and requesting papal arbitration in the Moechian controversy. His half-hearted leadership of the campaign against the Bulgars resulted in defeat in the Battle of Versinikia. The stratēgos of the Anatolic Theme, Leo the Armenian, a popular and successful general, abandoned Michael on the battlefield but was proclaimed emperor by the military, in what was the last military overthrow of an emperor in Byzantine history. Michael was pressured to abdicate, and he retired to a monastery. His sons were castrated to prevent the continuation of his dynasty.

Leo V the Armenian (Greek: Λέων ὁ Ἀρμένιος, Léōn ho Arménios; c. 775 – 25 December 820) was the Byzantine emperor from 813 to 820. He is chiefly remembered for ending the decade-long war with the Bulgars, as well as initiating the second period of Byzantine iconoclasm.

A senior general of Armenian origin, Leo distinguished himself under Nikephoros I and Michael I Rhangabe, eventually becoming the stratēgos of the Anatolic Theme. Taking advantage of Michael's defeat at the Battle of Versinikia, he forced the emperor to abdicate in his favour. He was able to withhold the blockade of Constantinople by Krum of Bulgaria and, after Krum's death, concluded a 30-year peace with his successor Omurtag.

Staurakios or Stauracius (Greek: Σταυράκιος, romanized: Staurákios; early 790s – 11 January 812) was the shortest-reigning Byzantine emperor, ruling for 68 days between 26 July and 2 October 811.

He was born in the early 790s, probably between 791 and 793, to Nikephoros I and an unknown woman. Nikephoros seized the throne of the Byzantine Empire from Empress Irene in 802, and elevated Staurakios to co-emperor on 25 December 803. On 20 December 807, a bride show was held by Nikephoros to select a wife for Staurakios, which resulted in his marriage to Theophano of Athens, a kinswoman of Irene. Little else is known of him until he came to take the throne upon the death of Nikephoros.

Irene of Athens (Greek: Εἰρήνη, Eirḗnē; 750/756 – 9 August 803), surname Sarantapechaena (Greek: Σαρανταπήχαινα, Sarantapḗchaina), was Byzantine empress consort to Emperor Leo IV from 775 to 780, regent during the childhood of their son Constantine VI from 780 until 790, co-ruler from 792 until 797, and finally empress regnant and sole ruler of the Eastern Roman Empire from 797 to 802. A member of the politically prominent Sarantapechos family, she was selected as Leo IV's bride for unknown reasons in 768. Even though her husband was an iconoclast, she harbored iconophile sympathies. During her regency, she called the Second Council of Nicaea in 787, which condemned iconoclasm as heretical and brought an end to the first iconoclast period (730–787). Irene's concluding five years of sole rule were unprecedented in Roman and Byzantine history. Her public figure in this period was polarizing, due to the setbacks faced by the Empire and her iconophilic stances, often attributed to her gender and the influence of her retinue.

After the death of her husband, Irene secured the throne for her family, setting herself in charge. During her regency with Constantine VI, she became very influential in government policies, largely overshadowing her son. As Constantine VI reached maturity, he began to move out from under the influence of his mother. In the early 790s, several revolts attempted to proclaim him as sole ruler. One of these revolts succeeded, but in 792 Irene was re-established in all imperial powers as "co-emperor" with Constantine VI. In 797, Irene organized a conspiracy in which her supporters gouged out her son's eyes. Constantine was imprisoned and probably died shortly afterwards. With him out of the way, Irene proclaimed herself sole ruler. Pope Leo III—already seeking to break links with the Byzantine East—used Irene's alleged unprecedented status as a female ruler of the Roman Empire to proclaim Charlemagne as Emperor of the Romans on Christmas Day of 800 under the pretext that a woman could not rule solely and thus the Roman throne was actually vacant. A revolt in 802 overthrew Irene and exiled her to the island of Lesbos, supplanting her on the throne with Nikephoros I. Irene died in exile less than a year later.

Bardanes, nicknamed Tourkos, "the Turk" (Greek: Βαρδάνης ὁ Τοῦρκος, romanized: Bardanēs ho Tourkos, fl. 795–803), was a Byzantine general who launched an unsuccessful rebellion against Emperor Nikephoros I (r. 802–811) in 803. Although a major supporter of Byzantine empress Irene of Athens (r. 797–802), soon after her overthrow he was appointed by Nikephoros as commander-in-chief of the Anatolian armies. From this position, he launched a revolt in July 803, probably in opposition to Nikephoros's economic and religious policies. His troops marched towards Constantinople, but failed to win popular support. At this point, some of his major supporters deserted him and, reluctant to engage the loyalist forces in battle, Bardanes gave up and chose to surrender himself. He retired as a monk to a monastery he had founded. There he was blinded, possibly on Nikephoros's orders. He was of Turkic origin