In the confrontation between the Christian kingdoms of the north and the Muslims of Al-Andalus, the kingdom of Alfonso VI was particularly significant; the Christian armies finally won important cities south of the Duero (Salamanca, Ávila, Segovia, Sepúlveda) as well as Toledo. These were the last two decades of the 11th century, the time of El Cid. They were warlike times, of great insecurity, so that in Ávila everything relating to war was very prestigious. It is worth bearing in mind that the Muslims were still relatively close and made sporadic counter-attacks (in 1109 they recaptured nearby Talavera). The exact chronology of the erecting of the Walls of Ávila is not known. Chronicles written in later years and local tradition say that building was begun at the end of the 11th century and that the work lasted nine years. However, it is difficult to believe that with the small population of the city and its weak economy in those early decades, coupled with the political and social instability of the time, it would have been possible to erect in such a short time the 2516 metres of perimeter, with an average thickness of 3 metres and a height of 12 metres, and the 88 towers or round turrets.
It would have been a huge task, notwithstanding the fact that in many sections of the wall they re-used blocks of stone fashioned in Roman times which came from the necropolis, from civil constructions or even from the old Roman or Visigoth wall. We know that from 1135 onwards the city began a process of political consolidation and economic prosperity. This circumstance, together with other historical indicators, has led the most recent studies to claim that, although there was a modest wall from the very beginning of the conquest in 1085, the current wall is a work of the second half of the 12th century. In fact, a royal document from 1193 alludes to the fact that in that year construction was taking place on the “fortress and the powerful towers ... to defend oneself from the incursions of enemies”. Around the same time (in addition to Notre Dame in Paris) the walls of Salamanca, Segovia and Soria were being erected. These fortified Castilian cities served both to prevent the Muslims from advancing through the natural passages of the “Sistema Central” mountain range and as a base for the Christian knights from which to raid Muslim lands.