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.