By the 11th Century, Christianity had secured a stable base across most of Europe. However the Byzantine Empire was on the very periphery of Christendom and faced continuous threats from Muslim conquests. The city of Jerusalem had been in Muslim hands since 638, but ongoing wars between different Arab dynasties had resulted in it being captured by the Seljuks in 1076. When their army began threatening to attack Constantinople, the Byzantine Emperor Alexios I Komnenos appealed to the Pope for assistance. Many historians have since argued that Urban II took advantage of the situation as a way to reunite Christendom under his papacy, which was facing a threat from the Antipope Clement III. No accurate record exists of how many people responded to the Pope’s call, but estimates suggest anywhere between 60,000 and 100,000 people joined the First Crusade. A large number of these were ordinary peasants. Exactly why so many people chose to ‘take the cross’ is also a question subject to fierce debate. Some nobles probably went in the hope of seizing riches along the way, but a large number of Crusaders almost certainly did so out of Christian piety. Although Pope Urban had intended the Crusade to depart on 15 August 1096, large numbers of peasants and low-ranking knights set off earlier on what became known as the People’s Crusade. This group of Crusaders were generally poorly disciplined and had been given little to no military training. They killed thousands of Jews in the pogroms of 1096 before they even left Europe.