The Dom Luís I Bridge is a double-deck metal arch bridge that spans the River Douro between the cities of Porto and Vila Nova de Gaia in Portugal. At its construction, its 172m span was the longest of its type in the world. It has been confused with the nearby Maria Pia Bridge, a railway bridge that was built 9 years earlier, that is similar in aspect to the Dom Luís bridge.HistoryIn 1879, Gustave Eiffel presented a project to construct a new bridge over the Douro, with a single deck in order to facilitate navigation. This project was rejected due to dramatic growth of the urban population, which required a re-thinking of the limits of a single-deck platform.A competition was initiated in November 1880, in order to construct a double-deck metal bridge, which included projects by Compagnie de Fives-Lille, Cail & C., Schneider & Co., Gustave Eiffel, Lecoq & Co., Société de Braine-le-Comte, Société dês Batognolles (which submitted two ideas), Andrew Handyside & Co., Société de Construction de Willebroek (also two projects) and John Dixon. It was in January of the following year that deliberations by the committee supported the project of Société de Willebroek, a design that cost 369 000$000 réis, and provided better conditions. On 21 November 1881, the public work was adjudicated to the Belgian society Société Willebreck, from Brussels, for 402 contos, and administrated by Théophile Seyrig, a disciple of Gustave Eiffel, and author of the project. Consequently, the design resembled that of the D. Maria bridge. Construction began on the Ponte D. Luís I, along the flanks of the towers of Ponte Pênsil, but were disassembled.