In 1394, Bayezid laid siege to Constantinople, the capital of the Byzantine Empire. Anadoluhisarı fortress was built between 1393 and 1394 as part of preparations for the second Ottoman siege of Constantinople, which took place in 1395. On the urgings of the Byzantine emperor Manuel II Palaeologus, a new crusade was organized to defeat him. This proved unsuccessful: in 1396 the Christian allies, under the leadership of the King of Hungary and future Holy Roman Emperor (in 1433) Sigismund, were defeated in the Battle of Nicopolis. Bayezid built the magnificent Ulu Cami in Bursa, to celebrate this victory.