the leaders of Banū Naḍīr who then killed their hosts. Muhammad's victory over the Jews of Khaybar in the subsequent battle was also aided by the distance of the settlements and their castles from one another, the absence of coordination between the fighting forces, the death of the leader Sallām ibn Mishkam, and a Jew who showed the Muslims the secret entrances to one of the fortresses. The castles of Khaybar had tunnels and passages which in wartime enabled the besieged to reach water sources outside the castles. Between 16 to 18 Muslims and 93 Jews were killed. After the Muslim victory, Muhammad, concerned that Khaybar would remain desolate and would not continue supplying its agricultural produce to the Hejaz, signed an agreement with the Jews which allowed many of its inhabitants to remain on their lands, while requiring payment of half their crops to the conquerors. Aftermath Captives of war and slaves from other countries were brought to Khaybar and the people of Hejaz became more accustomed to agriculture. Jews continued to live in the oasis for several more years afterwards until they were finally expelled by caliph Umar, who decided to expel the Jews of Khaybar in 642 under the pretense that before his death Muhammad had commanded that two religions could not exist simultaneously in the Hejaz. The imposition of tribute upon the conquered Jews of the Khaybar Fortress served as a precedent. Islamic law came to require exaction of tribute known as jizya from dhimmis, i.e. non-Muslims under Muslim rule. For many centuries, the oasis at Khaybar was an important caravan stopping place. The center developed around a series of ancient dams built to hold run-off water from the rain. Around the water catchments, date palms grew. Khaybar became an important date-producing center. Expulsion of the Jews During the reign of Caliph Umar (634–644), the Jewish community of Khaybar were transported alongside the Christian community of Najran to the newly conquered regions of Syria and Iraq; Umar also forbade non-Muslims to reside in the Hejaz for longer than three days. Since then, the Jews of Khaybar traveled around many areas throughout the Islamic Empire as artisans and merchants and maintained a distinctive identity until the 12th century. The Journey of Benjamin of Tudela Benjamin was a Jew from Tudela in the Kingdom of Navarre. He travelled to Persia and Arabia in the 12th century. He visited