Made of iron, arched Luis I bridge over the river Douro connects the Portuguese cities of Porto and Vila Nova de Gaia. At the time of construction, the span length of the bridge was 172 feet, and the bridge was the longest in the world.

For the construction of the iron bridge over the river Douro, the Portuguese government announced a competition. The bridge was to be built next to the existing bridge and replace it. In this competition took part théophile Seyrig, engineer and designer. He also participated in the construction of the bridge Donna Maria Pia, when he was a partner of Gustave Eiffel. During this time he participated in one contest and won it.

The construction of the Luis I bridge was begun in 1881 and lasted about five years. Grand opening of the automobile and the pedestrian bridge was held on 31 October 1886. The bridge is two levels, and each level has pedestrian walkways. From the upper level offers stunning views of the city, on the lower tier you can watch the boat traffic on the river. The total length of the bridge – 385, 25 m, weight 3,045 tone, the length of the arch – 172 metres, and its height – 44, 6 meters.

It was originally planned that the traffic on the roads of the bridge will be on both levels of the bridge. At different times the upper level of the bridge were trams, and on the lower trolley. Today runs one of the top lines of the metro (line E) of the city of Porto, also has pedestrian walkways, and below – the roadway for cars.

It should be noted that the bridge Luis I in-kind is a symbol of the city of Porto and the image of the bridge is very often found on the labels of bottles of local wine.