Until now, London Bridge has been the only metropolitan bridge over the Thames. The nearest bridge up stream is several miles away, at Putney. The City of Westminster and the suburbs around it have been growing fast. In 1738 Charles Labelye, a Huguenot engineer from Switzerland, was appointed to build a new bridge at Westminster.
To construct the piers that support his bridge, Labelye used a new technique. He had a 'caisson' built for each pier, a huge box of timber that was floated into position in the river. The stone pier was then built inside it and the weight of the masonry slowly forced the caisson to the bottom, into a pit dug into the river bed. When the pier was finished, the wooden sides of the caisson were removed. Only the bottom was left, buried beneath the pier.
There are problems with Labelye's ingenious new technique. On one side of the river the bed is of gravel, and there the piers have stayed firm. On the other side the bed is of shifting sand. Even while the bridge was being built, problems arose when one pier started to lean to one side. The pier has been rebuilt, but the weakness in the design is fundamental. In Victorian times Labelye's bridge will be replaced by the present Westminster Bridge.