Actually this is partially correct. The original mouth of the Ouse was its current position, a small Roman port existed there that served the agricultural areas around Ripe and Chalvington - the minor Roman road serving the two places ran across Heighton Hill where its agger is still very...
Sandwich, Dover, Hythe, Romney and Hastings were the five original ports that made up the Cinque Ports. Others such as Rye, Winchelsea and Seaford later became limbs of one of the five ports. Newhaven was never part of it.