Alcántara Bridge, Extremadura, Spain

Trajan's granite bridge striding across the Tagus gorge at Alcántara, with the small Roman triumphal arch standing on its central pier. It was designed by Caius Julius Lacer and built between AD 104 and 106. This is Roman bridge building at its most ambitious: six arches, the largest of them enormous, carrying the roadway high above the river on piers of dry-laid stone. Its strategic position made it a target, and armies broke its arches in 1214, 1760, 1809 and 1836. Each time it was patched up, and a full rebuild of the broken arch around 1860 restored the profile you see here. A small Roman temple still stands at one end.