The Luís I Bridge (Ponte Luís I) is a metal arch bridge that spans the Douro River between the cities of Porto and Vila Nova de Gaia in Portugal. At the time of construction its span of 172 m was the longest of its type in the world.
The Government held a competition for the construction of a metallic bridge over the Douro River on a site that was adjacent to an existing bridge and would replace it. Téophile Seyrig had already engineered the D. Maria Pia Bridge project nearby, whilst working as a partner of Eiffel. He now took sole responsibility for the new, major Luís 1st Bridge. The construction was begun in 1881 and the bridge opened on 31 October 1886.
Total length 385.25 m
Weight 3045 tons
The arch measures 172 m in length and 44.6 m in height
Originally built to take road traffic on both decks, at various times it saw trams on the upper and trolleybuses on the lower. The top deck is now occupied by Line D of the Metro do Porto and a pedestrian walkway.