The Bridge of Alcántara was situated on the Emérita-Brácara Way which was part of the network of Roman roads of Hispania. However, this impressive work of engineering was not a public construction paid by the Roman state. In ancient Rome the bridges, Opus Pontis, were the responsibility of each region. The Bridge of Alcántara was therefore paid for by fourteen municipalities.
The site chosen on which to build it was a narrow section of the Tajo since the force of its flow was there not so great. The striking verticality of the bridge is due to the fact that the level of the water may rise considerably. The imposing Alcántara Bridge was erected probably between 95 and 105 A.D. and was the work of the Roman architect Gaius Julius Lacer. The bridge is 197 metres long and is supported by five pillars of different heights which are adapted to the relief of the terrain. The width of its two central arches is still impressive today: some 48 metres. Only two of these supports are anchored in the river, which means that at low water level the remainder of the supports are protected from the current. This is one of the reasons for its optimum state of preservation.
In the Alcántara Bridge Roman engineering shows its great ability for building perennial infrastructures. The bridge stands on solid pillars covered by dressed ashlars arranged by alternating the longer sides (stretchers) with the shorter sides (headers); this technique was later used by the Arabs. The dimensions are 60×120 cm. The result is harmonious and precise.