Six remarkable bridges span the banks of the Douro. These include Ponte Maria Pia, a railway bridge built by Gustave Eiffel, the most elegant, with its single arch with a 350m span; the Ponte de Dom Luís I, built in 1886, which is the symbol of Porto and forms part of the UNESCO World Heritage zone and the Ponte da Arrábida highway bridge, built in 1963, which crosses the Douro in a single reinforced concrete arch of around 270m.