In 1875, the
Royal Portuguese Railway Company announced a competition for a bridge to carry the Lisbon to Porto railway across the river Douro. This was very technically demanding: the river was fast-flowing, its depth could be as much as during times of flooding, and the riverbed was made up of a deep layer of gravel. These factors ruled out the construction of piers in the river, meaning that the bridge would have to have a central span of 160m (525 ft). At the time, the
longest span of an arch bridge was the 158.5m (520 ft) span of the
bridge built by
James B. Eads over the
Mississippi at
St Louis. When the project was approved, João Crisóstomo de Abreu e Sousa, member of the
Junta Consultiva das Obras Públicas (
Consultative Junta for Public Works), thought that the deck should have two tracks.
Gustave Eiffel's design proposal, priced at 965,000 French francs, was the least expensive of the four designs considered, at around two-thirds the cost of the nearest competitor. Since the company was relatively inexperienced, a commission was appointed to report on their suitability to undertake the work. Their report was favorable, although it did emphasise the difficulty of the project: Responsibility for the actual design is difficult to attribute, but it is likely that
Théophile Seyrig, Eiffel's business partner who presented a paper on the bridge to the Société des Ingénieurs Civils in 1878, was largely responsible. In his account of the bridge that accompanied the 1:50 scale model exhibited at the
1878 World's Fair, Eiffel credited Seyrig and
Henry de Dion with work on the calculations and drawings. Construction started on 5 January 1876. Work on the abutments, piers, and approach decking was complete by September. Work then paused due to winter flooding, and the erection of the central arch span was not re-started until March 1877. By 28 October 1877, the platform was mounted and concluded, with the work on the bridge finishing on 30 October 1878. ==Architecture==