Why did construction of the Cordouan Lighthouse take 27 years?

The construction of the Cordouan Lighthouse took 27 years primarily due to the subsidence of the island upon which it was being built.1

When the engineer and architect Louis de Foix began the project in 1584, the site was an island; however, the ground proved unstable, and by the time the ambitious structure was completed in 1611, the island had become completely submerged at high water. This challenge transformed the project into the first lighthouse ever built in the open sea, serving as a significant precursor to later rock structures like the Eddystone Lighthouse.12