RICHBOROUGH ROMAN FORT, Sandwich, Kent. Aerial view. Richborough, or 'Rutupiae' was known to be a major naval base This shows the triple ditch defences of the early 3rd century fort surrounding the concrete base of the 1st century monumental arch. All of these are surrounded by the outer defensive wall of a Saxon Shore fort - the bases of the 'Classis Britannica' the Roman fleet based around the coast of Britain.