In 627, the Meccans, accompanied by tribal allies as well as the Banu Nadir - who had been very active in supporting the Meccans - marched against Medina - the Muslim stronghold - and laid siege to it. It is unclear whether their treaty with Muhammad obliged the Qurayza to help him defend Medina, or merely to remain neutral, according to Ramadan, they had signed an agreement of mutual assistance with Muhammad. The Qurayza did not participate in the fighting - according to David Norcliffe, because they were offended by attacks against Jews in Muhammad's preaching - but lent tools to the town's defenders. According to Al-Waqidi, the Banu Qurayza helped the defense effort of Medina by supplying spades, picks, and baskets for the excavation of the defensive trench the defenders of Medina had dug in preparation. According to Watt, the Banu Qurayza "seem to have tried to remain neutral" in the battle but later changed their attitude when a Jew from Khaybar persuaded them that Muhammad was sure to be overwhelmed and though they did not commit any act overtly hostile to Muhammad, according to Watt, they entered into negotiations with the invading army.