aerial photograph of Caister Roman Fort in Caister-on-Sea Norfolk England UK. Constructed sometime around 200AD Casiter Roman fort was one of the Saxon Shore forts built to defend against attacks by Saxons.It was in use until the Romans abandoned England in the 4th Century. In Roman times the fort was on an Island surrounded by estuary which has now largely dried up. Another Fort, Burgh Castle, was built on the other side of the estuary.