Conical structure for Cherbourg harbour

From the 16th century onwards there were successive projects to protect the port of Cherbourg, strategically located opposite England. In 1781 Louis Alexandre de Cessart, a roads and bridges engineer with a reputation in the marine domain, proposed building a sea wall composed of ninety conical islets some 20 metres high with a base 48 metres in diameter, linked by heavy chains. Wooden structures were built on land then towed and sunk on site to serve as armatures for rocks and masonry. An initial scaled-down trial was conclusive, and on 22 June 1786 Louis XVI went to Cherbourg to watch the immersion of the ninth cone. However, the fragility of these structures and the problems this posed put an end to this costly enterprise. By the beginning of the French Revolution, only eighteen of these caissons had been installed. The project was abandoned for a traditional sea wall, completed in 1853. This model may have been in one of the royal collections seized during the Revolution.