The Cathedral of Ávila has Romanesque and Gothic architectural traditions. It was planned as a cathedral-fortress, its apse being one of the turrets of the city walls. It is surrounded by a number of houses or palaces.
It is not known exactly when the construction of the Cathedral began, there being two theories. One states that Alvar García started its construction in 1091 inside the remains of the Church of the Saviour, which was in ruins as a result of successive Muslim attacks, and that Alfonso VI of Castile raised the money necessary to build it. Other historians believe the Cathedral to be the work of the maestro Fruchel in the 12th century coinciding with the repopulation of Castille led by Raymond of Burgundy.
Of the 13th century are the first stages of the towers and aisles and of the 14th century the second stage of the towers, the cloister, the vaults and the flying buttresses. Already in the 15th century the cathedral was complete and in 1475 Juan Guas built the mechanical clock.
The Cathedral of Ávila is considered by its age (12th century), along with the Cathedral of Cuenca, as the first two Gothic cathedrals in Spain. It shows French influences and great resemblances to the Abbey Church of St Denis, the first European Gothic church.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.