Ali's stay in Basra was not long. Having appointed Abdullah bin Abbas as the governor, Ali repaired to Kufa in 36/657 and made it the seat of his government and the capital. The word kufa means, a spot where pebbles and sand are found in admixture, and as the site answered to this description. It will be worthwhile to mention that Kufa in Iraq was founded in the year 17/638, about three years after caliph Umar bin Khattab assumed the caliphate at Medina. It was used as a garrison town during Umar's time, where different contingents from distant places could stay and should be readily available in an emergency. The city was organised into seven tribal contingents divided into seven military districts. This grouping continued for 19 years until it underwent another change in 37/657, when Ali came to Kufa. So great was Umar's interest in Kufa that he described it as "tower of Islam" (qubbat al-Islam), and "the head of the people of Islam" (ras ahl al-Islam). In describing the settlers of Kufa, he according to Ibn Sa'd (6th vol., p. 7) said, "They are the lance of God, the treasure of faith, the cranium of the Arabs, who protect their own frontier forts and reinforce other Arabs." It may be pointed out that these epithets of honour and distinction were not accorded to any other city, such as Damascus or Basra. The selection of Ammar bin Yasir as the governor of Kufa, and Abdullah bin Masud as deputy governor to the leadership of Kufa reveals Umar's intention to replace tribal claims with Islamic claims. After Umar's death, Uthman appointed Walid bin Uqba as a governor of Kufa in 25/646. Apprehensive of Muawiya's designs against him, Ali considered Kufa suitably situated to check any encroachment in Iraq, therefore he made it his capital, as topographically it was in the centre of his dominions.