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, so that the bridge would have to have a central span of 160m (525 ft). At the time the longest bridge span was the 158.5m (520 ft) 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") considered that the deck should have two lanes.