For reasons of conditioning with the route of the wall of the city, which is attached to the temple, the apse of the Cathedral of Avila becomes part of it, getting your setup the character of a more defensive tower.
It is for this reason is presented abroad as a stout curved wall topped by two orders of battlements behind which is just between the buttresses necessary, the top exterior of the Chapel.
This problem has resulted in a certain incongruity between the internal organization of the head of the church and the exterior treatment of the apse, popularly called " cimorio "- in whose walls encyst five chapels that open onto an ambulatory dual spacecraft separated by eight columns around behind the Chapel.
Under the line of the battlements are simple buttresses alternating with thin columns, whose space is denoted the perimeter polygonal apse.