© All Rights Reserved The 1876 Dona Maria Pia bridge in Porto. Designed by Gustave Eiffel, the bridge is the only one of the six bridges spanning the Douro that is not usedRelated images Avenida de Dom Carlos I - Foz - Porto Porto Monument Rua de Miguel Bombarda paving Porto Bridge Glimpse Crystal Palace Super Bock Arena - Porto Praia Caneiro - Porto