© 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 River Douro from Porto Tram Avenida do Brasil - Porto Houses in the Ribeira - Porto Crystal Palace Super Bock Arena - Porto Porto Cathedral Square Porot - Bishop's Palace and Luis I Bridge