The Dom Luís I Bridge or Luís I Bridge is a double-deck metal arch bridge that spans the River Douro between the cities of Porto and Vila Nova de Gaia in Portugal. At its construction, its 172 meters span was the longest of its type in the world. It has been confused with the nearby Maria Pia Bridge, a railway bridge that was built nine years earlier (and located 1 kilometer) to the east), that is similar in aspect to the Luís I bridge. In 1879, Gustave Eiffel presented a project to construct a new bridge over the Douro, with a single deck to facilitate navigation. This project was rejected due to the dramatic growth of the urban population, which required a re-thinking of the limits of a single-deck platform.

Photo By Deensel - Dom Luís I Bridge, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=62390122