December 25, 820: Emperor Leo V is murdered; Michael II succeeds him on the throne
After December 25, 820: The tourmarch of the Foederati, Thomas the Slav, rebels against Michael II in the Anatolic theme
Spring of 821: Thomas campaigns against the Arabs and successfully negotiates an alliance with the Arab caliph al-Mamun
October-November of 821: Thomas transports his troops to Thrace
December of 821: Thomas begins his attack on Constantinople by land and sea. Constantinople is under siege
Winter of 821-822: Military operations around Constantinople are discontinued due to the rough weather conditions
Spring of 822: Thomas resumes his offensive on Constantinople
November of 822: The Bulgarians under Omurtag invade the Byzantine lands and clash with the forces of Thomas on the plain of Kedouktou
Winter of 822-823: Thomas spends the winter on the plain of Diabasis
Spring of 823: Thomas’ troops conduct raids in Thrace
April-early May of 823: Thomas is defeated by Emperor Michael II on the plain of Diabasis and seeks refuge in Arcadiopolis
Late spring-mid March October of 823: Emperor Michael II besieges Arcadiopolis
mid-October 823: Thomas is handed over to Michael II by the citizens of Arcadiopolis and is put to death
After February of 824: The imperial forces capture Panion and Heraclea
Early March of 824: Michael II makes his triumphal return to Constantinople