had not some of its leaders been sympathetic towards Islam. The Bani Amir, who had a pact with Muhammad, refused to join. Other tribes included the Banu Murra, with 400 men led by Hars ibn Auf Murri, and the Banu Shuja, with 700 men led by Sufyan ibn Abd Shams. In total, the strength of the Confederate armies, though not agreed upon by scholars, is estimated to have included around 10,000 men and six hundred horsemen. In December 626 the army, which was led by Abu Sufyan, marched on Medina. In accordance with the plan, the armies began marching towards Medina, Meccans from the south (along the coast), and the others from the east. At the same time, horsemen from the Banu Khuza'a left to warn Medina of the invading army. Muslim defence The men from Banu Khuza'a reached Muhammad in four days, warning him of the Confederate armies that were to arrive in a week. Muhammad gathered the Medinans to discuss the best strategy of overcoming the enemy. Meeting the enemy in the open (which led to victory at Badr), and waiting for them inside the city (a lesson learned from the defeat at Uhud) were both suggested. Ultimately, the outnumbered Muslims opted to engage in a defensive battle by digging deep trenches to act as a barrier along the northern front. The tactic of a defensive trench was introduced by Salman the Persian. Every capable Muslim in Medina including Muhammad contributed to digging the massive trench in six days. The ditch was dug on the northern side only, as the rest of Medina was surrounded by rocky mountains and trees, impenetrable to large armies (especially cavalry). The digging of the ditch coincided with a near-famine in Medina. Women and children were moved to the inner city. The Medinans harvested all their crops early, so the Confederate armies would have to rely on their own food reserves. Muhammad established his military headquarters at the hillock of Sala' and the army was arrayed there; this position would give the Muslims an advantage if the enemy crossed the trench. The final army that defended the city from the invasion consisted of 3,000 men, and included all inhabitants of Medina over the age of 14, except the Banu Qurayza (the Qurayza did supply the Muslims with some instruments for digging the trench). According to Irfan Shahid, the Muslims adopted the tactic of