The capture of Thessalonica, traditionally the second city of the Byzantine Empire after Constantinople, allowed Theodore to challenge the Nicaean claims on the Byzantine imperial title. With the support of the bishops of his domains, he was crowned emperor at Thessalonica by the Archbishop of Ohrid, Demetrios Chomatenos. The date is unknown, but has been placed either in 1225 or in 1227/8. Having openly declared his imperial ambitions, Theodore turned his gaze onto Constantinople. Only the Nicaean emperor John III Doukas Vatatzes, and the Bulgarian emperor Ivan II Asen were strong enough to challenge him. In a bid to preempt Theodore, the Nicaeans seized Adrianople from the Latins in 1225, but Theodore quickly marched into Thrace and forced the Nicaeans to leave their European possessions to him. Theodore was free to assault Constantinople, but for unknown reasons delayed this attack. In the meantime, the Nicaeans and Latins had settled their differences, and although formally allied with Theodore, Ivan II Asen also entered talks for a dynastic alliance between the Latin Empire and Bulgaria. In 1230, Theodore finally marched against Constantinople, but unexpectedly turned his army north into Bulgaria instead. In the ensuing Battle of Klokotnitsa, Theodore's army was destroyed and he himself taken captive and later blinded.