Made of iron, arched bridge of Luis I over Douro river joins the Portuguese city of Porto and Vila Nova de Gaia. At the time of construction of the span length of the bridge is 172 meters, and the bridge is the longest in the world.

The construction of the iron bridge over the river Douro Portuguese Government has announced a competition. The bridge was to be built next to the existing bridge and replace it. This competition was attended by Theophile Seyrig, an engineer and designer. He also participated in the construction of the bridge Donna Maria Pia, where he was a partner Gustave Eiffel. During this time he participated in a contest and won it.

Luis I Bridge construction began in 1881 and lasted for about five years. Inauguration of the road and pedestrian bridge was held October 31, 1886. Bridge - a two-level, and at every level have pedestrian sidewalks. On the upper level offers a spectacular view of the city, on the lower tier is possible to observe the movement of the boats on the river. The total length of the bridge - 385, 25 m, weighs 3045 tons, the length of the arch - 172 meters, 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 various times, on the upper level of the bridge trams, and the bottom - trolley. Today, on top passes one of the subway lines (line A) of the city of Porto, is also a pedestrian sidewalk, and at the bottom - the roadway for cars.

It is worth noting that the Bridge Luis I in-kind is a symbol of the city of Oporto, and the image of the bridge is very often found on the labels of bottles of the local port.