Reports of the renewed killing of Christian pilgrims, and the defeat of the Byzantine Empire by the Seljuqs, led to the First Crusade. Europeans marched to recover the Holy Land, and on July 15, 1099, Christian soldiers were victorious in the one-month Siege of Jerusalem. In keeping with their alliance with the Muslims, the Jews had been among the most vigorous defenders of Jerusalem against the Crusaders. When the city fell, the Crusaders slaughtered most of the city's Muslim and Jewish inhabitants, leaving the city "knee deep in blood".