In 1776, King Louis XVI of France appointed a commission to find a strategic port to defend the coasts of the English Channel. The goal was to build a war port that could face England directly, and the town of Cherbourg was chosen for this task. To protect the harbor, the monarchy initially used 90 wooden cones filled with stones. However, construction was abandoned in 1788, leaving the harbor vulnerable. In 1784, Louis XVI approved a new and unusual project by an engineer named Cessart. His idea was to build a 20-meter-high wooden truncated cone dike in the open sea on a sandy seabed. The first four cones were unable to withstand the storms, and in five years, only about twenty out of ninety were completed. The failure in 1788 led to the abandonment of Cessart's project in favor of a more traditional method proposed by another engineer, La Bretonnière, who suggested sinking old ships and scattering stones to protect the harbor. The goal was to build a war port capable of holding 80 warships, and the project was overseen by notable figures such as Suffren, Dumouriez, and La Bretonnière. La Bretonnière's plan called for a 4-kilometer dike between the island of Pelée and the tip of Querqueville, but the royal court chose Cessart's unconventional design instead. Cessart's dike was to consist of 90 wooden cones, each about 50 meters in diameter at the base and 20 meters at the top, with a height of 20 to 24 meters. Each cone was towed out to sea, sunk, filled with stones, and connected to others with iron chains. The first cone was sunk on June 6, 1784, one kilometer from the island of Pelée. The harbor was filled with 300 to 400 boats ferrying stones from the port of Becquet. The structures were made of oak and beech, with openings at multiple levels to pour the stones regardless of the tide. Louis XVI made his only trip to the provinces on June 22, 1786 (some sources say June 23) to attend the launching of the ninth cone. No French king had ever made such a long journey to watch a construction site. However, the project faced significant challenges due to weather conditions. As noted by the 19th-century historian Alexis de Tocqueville, the cones could only be launched two or three months a year, and only on a few days each month, resulting in a maximum of thirty-six days of favorable weather per year for the entire project. By 1788, the sea had proven too strong. The first four cones were destroyed by storms, and the remaining ones suffered serious damage. In five years, only about twenty cones were completed out of the planned 90 (some sources mention 18). Cessart tried to protect the cones by surrounding them with large masses of stones, a solution that contradicted the original design. In 1788, it was concluded that Cessart's approach had failed, and the cones were left empty. The project then returned to La Bretonnière's method, which had previously been rejected. The concern was that the stones might be pushed into the harbor itself. The contrast was stark: an avant-garde project was abandoned in favor of a more traditional, rustic technique. The consequences were felt in the city, as the abandonment of the cones led to unemployment in Cherbourg on the eve of the French Revolution, and funding was cut in 1790. La Bretonnière's resignation in 1792 halted the work for ten years. A local historian, Magali Lachèvre, argues that the failure of this project weakened the monarchy and may have accelerated the arrival of the 1789 Revolution. While the judgment is clear, it also highlights the financial strain on a kingdom already burdened by debt. The offshore dike, however, was not completed until 1853, about 70 years after the first cone was sunk. It measures 3,640 meters, with an average width of 100 meters at its base, 12 meters at its top, and a height of 27 meters. The eastern and western dikes were added in the 1890s. Engineers who worked on the project included Cessart, La Bretonnière, Joseph Cachin, then Fouques-Duparc and Félix Reibell until 1853. The dikes and forts have been designated as Historical Monuments since 2021. Of Cessart's cones, only models remain. The Musée des Arts et Métiers preserves a wooden and iron model of 38 x 85 cm, which entered its collections in 1849.