A major problem that plagued St Petersburg for almost the first two centuries of its existence was how to construct permanent bridges over its wide, deep, and fast-flowing main river.
The first bridges were pontoon bridges, sections of which could be detached to allow ships to pass. Such bridges were, however, liable to be swept away by flooding and also had to be dismantled for several weeks at a time when there were flows of ice on the river. The first pontoon bridge was built in 1727. The last was destroyed by fire in 1916.
The first metal bridge over the main river with spans supported by piers settled on the riverbed was Blagoveshchensky Bridge, built in 1847-1850.
Before that, however, in 1769-1774 the self-taught inventor and engineer Ivan Kulibin developed this daring design for a single-span, 298-metre-long bridge made of wood. The span reached a height of about 30 metres, allowing ships to pass underneath without the need for the bridge to be raised.
The viability of Kulibinís design was proven by extensive testing of a 1:10 scale model. However, for reasons that are not very clear, the bridge was never built. Kulibin went on to design a semaphore telegraph system, but this again was not implemented. Russiaís first telegraph was eventually set up 40 years later, to a French design.