Ponte Maria Pia crosses the Douro River located in the city of Porto in Portugal. The bridge was opened in 1877 by the King of Portugal and is named after Queen Maria Pia who lived from 1847 to 1911. The bridge is 563 meters long and has a span of 160 meters. The Maria Pia bridge was the world's largest arch bridge until the Garabit Viaduct opened in 1884.
Gustave Alexandre Eiffel was given the task of constructing the bridge. He is best known for the Eiffel Tower, but was also a skilled bridge engineer.
The construction of the bridge started in 1876. He used a new technique which meant that the bridge was completed more quickly. Construction started by building the arch from each side without support from below. Then a tower was built on each side of the river which was used to support the arch. Temporary wires were fixed in the rock, which went via the tower to the arch. As the arch grew, more wires were set up to hold the arch up. When the arch was finished, it stood by itself, and the wires were dismantled. This technique is used today on many bridges. At the same time as the arch became larger, the bridge track was built out from each side. This technique was used by Eiffel when he built the Garabit Viaduct.
The Maria Pia bridge has been used as a railway bridge until 1991 when St John took over the bridge.