You are correct John Walker, it is indeed the remains of the east gate's guard chamber of Reculver Roman Fort. Situated on the north Kent coast, it was positioned to protect the mouth of the Thames Estuary, whilst also the north opening to the former Wantsum Channel. It was the Wantsum Channel, which extended around the western and southern side of Thanet that gave it the title if 'Isle of Thanet' as it was once truly surrounded by water. The eastern end of the Channel was guarded by Richborough Roman Fort, but falling sea levels, silting and subsequent draining caused the former Channel to become grazing pasture.
There was not a recent archaeological excavation at Reculver, but a recent scheme of de-vegetation and consolidation of the walls enabled them to be exposed again.
Over to you John Walker