© 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 Ribeira - Porto Statue in Porto Ribeira - Another view... Number 18 Tram - Porto ArrĂ¡bida Bridge glimpse from Crystal Palace - Porto Ponte da Arrabida - Porto