The basic strategy of early Muslim armies on campaign was to exploit every possible weakness of the enemy. Their key strength was mobility. The cavalry had both horses and camels, the latter used as both transport and food for long marches through the desert ("e.g.", Khalid bin Walid's extraordinary march from the Persian border to Damascus). The cavalry was the army's main strike force and also served as a strategic mobile reserve. The common tactic was to use the infantry and archers to engage and maintain contact with the enemy while the cavalry was held back till the enemy was fully engaged. Once fully engaged, the enemy reserves were held by the infantry and archers, while the cavalry executed a pincer movement (like modern tank and mechanized divisions) to attack the enemy from the sides or to assault their base camps.