The Blue bridge spans the Moika River and joins together the Kazansky and Admiralty islands. The Blue bridge is the part of the Saint Isaac’s Square ensemble and it is the widest bridge in the world – 97.3 meters. In 1737 on the spot of the modern bridge the wooden draw one was built, which was painted in blue color, that is how it get its name. Since 1738 the bridge started to be called the Blue one. In 1805 it was reconstructed by the typical project of the single-bay cast-iron arched bridge with granite facing by the architect and engineer V. Geste. In 1842-1844 due to the construction of the Mariinsky Palace the bridge was widened up to the Antonenko Street. It is interesting that the Blue bridge is called invisible thanks to its width, which makes it look like a part of the square.