The Unusual History of Fort Boyard

Why this ambitious military project was repeatedly abandoned, and how it found unlikely fame in the world of TV and film

Image credit: Patrick Despoix CC-BY-SA 4.0

Looming out of the sea off the west coast of France is an eerie stone fortress. Cut off entirely from the mainland, the small castle appears to be impossibly floating on the waves, keeping watch over the military port of Rochefort and the Charente Estuary. In fact, Fort Boyard is fixed to a rocky bank, which at high tide is hidden entirely from view — an incredible feat of engineering that has stood for over 150 years, against all the odds.

At the end of the 17th century, plans were drawn up for a sea fort that could protect the military base at nearby Rochefort from enemy raids. However, the project was abandoned in 1692 after the enormous financial cost was realised. Sébastien Vauban, a distinguished French military engineer, said of the planned fort, “It would be easier to seize the Moon with your teeth than to attempt such an undertaking.”

During the Seven Years’ War (1756-63) new plans for the structure were made, but once again these were abandoned, and it was not until 1804 that the first foundations of Fort Boyard were finally laid. Piles of rubble and stone were sunk into the natural sand and stone bank to form a firm, flat base on which the fort could be built. This process alone was painstakingly slow, as work could only continue during the short hours of low tide when the bank is revealed. In the winter of 1807-8, disaster struck when these foundations were washed away by a series of powerful storms, and in 1809 construction work stopped altogether.

It wasn’t until 1857 that Fort Boyard was finally completed. Standing 20 metres high and armed with 74 cannons over three floors, the new fort resembled an impregnable battleship made of solid stone. Its oval design meant its guns could command a field of fire all across the surrounding area, protecting the harbour from any enemy incursions. It contained stores and living quarters to support an armed garrison of up to 250 soldiers.

Ironically, in the time it had taken to be built, increasingly long-range cannons had quashed Fort Boyard’s use as a credible naval defence. For a short time the building was therefore used as a prison, but by the turn of the century even this function was no longer required. The structure gradually fell into disrepair and ruin, until in 1990 it found an unlikely saviour. Fort Boyard became the filming location for a popular French game show of the same name, and received some much-needed restoration. Rendered redundant as a bulwark of France’s defence, the fortress’ newfound fame has, at least for now, secured its short-term future.

This article was originally published in How It Works issue 107, written by Tim Williamson

For more science and technology articles, pick up the latest copy of How It Works from all good retailers or from our website now. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, subscribe today!