The long stretch of shingle from Eastbourne to Pevensey Bay formed by the tidal wash of the sea. Creating in effect a natural sea wall that caused the sea to recede from the low lying land that reaches inland as far as Hailsham. The Crumbles used to be a haven for wild plants and breeding birds such as: Lapwing, Yellow wagtail, Partridge, Linnet, Meadow Pipit, Redshank, Reed Bunting, Common tern, Nightingale, to mention a few, but alas not for much longer.

These natural sea defenses are at present being turned into a Marina and a vast housing complex that is destroying the wildlife habitat. For over one hundred years shingle has been taken at the rate of around 250,000 tons per year for railway ballast and building materials. resulting in its height being reduced by 4 meters within 100 metres of the shore.

For centuries Pevensey and Willingdon levels were esturine, at some period since the Roman's the rivers silted up and a shingle spit evolved. The Crumbles is the third barrier to have formed in the last 10,000 years across this lowland, which mainly has been covered by the sea. It is estimated that it takes material 120 years to travel by longshore drift from Cornwall to Sussex.