The siege of Adrianople () in 813 was a part of the wars of the Byzantine Empire with the Bulgarian khan Krum (Byzantine-Bulgarian Wars). It began soon after the Byzantine field army was defeated in the battle of Versinikia on June 22. At first the besieging force was commanded by Krum's brother (whose name is not mentioned in the primary sources). The khan himself went on with an army to Constantinople. After an unsuccessful Byzantine attempt to murder him ruined all prospects for negotiations with them, Krum ravaged much of Eastern Thrace and then turned against Adrianople which was still under siege. The city—one of the most important Byzantine fortresses in Thrace—held out for a while despite being attacked with siege engines. Yet, without any help from outside, the garrison was forced