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9 March 2015 Last updated at 06:53 GMT
They crumble because of the weather and waves - it's called coastal erosion.
New research suggests it could lead to a billion pounds worth of property falling into the sea in the next 100 years.
Ayshah went to Winterton in Norfolk, one of the worst affected areas, to find out what its all about.

A summary of the above article is?
You might have seen pictures like these, empty homes in coastal areas that have slipped from cliffs that have become damaged.