All large ships are built, at St. Petersburg, in a dockyard off the Granite Quay, where the water is shallow; therefore a number of camels or caissons are kept at Cronstadt, for the purpose of carrying them down the river. Camels are hollow cases of wood, constructed in two halves, so as to embrace the keel, and lay hold of the hull of a ship on both sides. They are first filled with water and sunk, in order to be fixed on. The water is then pumped out, when the vessel gradually rises, and the process is continued until the ship is enabled to pass over the shoal. Similar camels were used at Rotterdam about 1690.