The Alconétar Bridge over the river Tagus at Alcántara Reservoir is part of the A-66 motorway. Formed by two twin 400 m long structures, its 220 m main span is a metal deck arch bridge. The construction system used was characterised by its speed and uniqueness, based on building large sized parts outside their final siting, their handling and their erecting using special auxiliary resources. Amongst the construction phases involved, lifting the two semi-arches into a vertical position and subsequently swivel lowering them for their crown closure is worthy of particular mention for its spectacular nature. This is the arch with the longest span built with this procedure in the world up to now.