A New Advent I saw a wonderful video with footage taken in part via drone of Mont St Michel off the coast of France.
It says by way of introduction:
After the construction of a raised causeway in 1859, Mont Saint-Michel was permanently connected to the adjoining land. That all changed in 2013, when the construction of a bridge allowed the fortified abbey to become an island once again.
Over there find also a description of Mont St-Michel and how it was a fortified abbey. The abbot was both religious and military commander.
Sounds like something we need again today.