The Islamization of Jerusalem refers to the process through which Jerusalem and its Old City adopted an Islamic atmosphere of influence and eventually a significant Muslim presence. The foundation for Jerusalem's Islamization was laid by the Muslim conquest of the Levant, and began shortly after the city was besieged and captured in 638 CE by the Rashidun Caliphate under Umar ibn al-Khattab, the second Rashidun caliph. The second wave of Islamization occurred after the fall of the Kingdom of Jerusalem, a Christian state that was established after the First Crusade, at the Battle of Hattin in 1187. The eventual fall of the Crusader states by 1291 led to a period of almost-uninterrupted Muslim rule that lasted for seven centuries, and a dominant Islamic culture was consolidated in the region