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.