PAN. Daylight. Exterior, view from southeast. The Romanesque basilica was erected between the 11th and 14th centuries, where according to tradition San Vicente and his sisters had been martyred in 303 AD. The city walls were constructed on the order of Alfonso VI in the 11th century. St. Vincent磗 Gate consists of an entrance arch between two towers. These towers are connected at the top by a bridge, which is unique amongst European city walls. Avila is a World Heritage Site of UNESCO.