Otto II's troops marched on Byzantine-controlled Apulia in January 982 with the purpose of annexing the territory into his Empire. Otto II's march caused the Byzantine Empire to seek an alliance with Muslim Sicily in order to hold on to its southern Italian possessions. Otto's army besieged and captured the Byzantine city of Taranto, the administrative center of Apulia, in March 982. After celebrating Easter in Taranto, Otto II moved his army westward, defeating a Muslim army in early July. Emir Abu al-Qasim, who had declared a Holy War ("jihad") against Otto, retreated when he noticed the unexpected strength of Otto II's troops when the latter was not far from Rossano Calabro. Informed of the Muslim retreat, Otto II left his wife Theophanu and young son Otto III (along with the Imperial treasury) in the city and marched his army to pursue the Muslim force.