2-370-045 - Samuel Magal/Sites & Photos/Heritage Images

San Vincent Gate, Avila, Spain, 2007. Avila's crenellated city walls are the best preserved in Spain. Built in the 11th and 12th century under Raymond of Burgundy, son-in-law of Alfonso VI, today they are 2.5 km long, 40 feet high and 10 feet thick, with approximately 2,500 battlements, 88 towers, 6 gates and 3 wicket gates. The fortification is the only instance of its kind of Medieval European architecture. The friezes and brick borders tell us that Mudejar and Moorish master builders also played a part in the walls' construction. The San Vicente Gate consists of an entrance arch between two immense parallel towers which flank it. These towers are connected at the top by a bridge which extends beyond the line of the walls. This bridge is unique amongst European city walls. There is no doubt that its principal function was to reinforce the defence of the gate. Avila was declared a World Heritage Site by UNESCO in 1985.