The wealth and influence of the abbey helped other foundations, for example St Michael's Mount in Cornwall. However, it started to become less popular as a centre of pilgrimage due to the Reformation. At the time of the French Revolution, there were almost no monks living there. The republicans closed the abbey. It became a prison. At first, this was to hold clerical enemies of the French republic. Later, there were also important political prisoners at the mount. In 1836, famous figures, such as Victor Hugo, started a campaign to restore the mount. The prison closed in 1863, and the mount became a historic monument in 1874. Mont-Saint-Michel and its bay became UNESCO World Heritage Sites in 1979. The factors for listing included cultural, historical, and architectural importance, as well as man-made and natural beauty.