A Saxon shore fort is a heavily defended later Roman military installation located in south-east England. Its most distinctive features are its defences, which are built on a massive scale, and incorporate certain structural elements such as tile and/or stone bonding courses in the walls, which are common to the defences of all monuments in this class. Also characteristic of the class as a whole is the tendency towards lack of standardisation between forts in respect of shape, size and design of component features. Saxon shore forts vary in size between 1.8-4 ha, and shapes range from square to polygonal to oval. Some of the rectangular examples may be confused with Roman forts, which continued to be occupied elsewhere in the country at the same time. They may be distinguished by the scale of their defences and by the lack of substantial remains of interior buildings, most of which are built of wood (wood had been superseded by stone as a building material in Roman forts in the 2nd century AD).

A total of nine surviving examples are known in England, along with the location of another which no longer exists and a few more possible examples. All are situated next to, or very close to, river estuaries or the open sea, between the Wash and the Isle of Wight in south-east England. Their purpose was to provide protection against seaborne Saxon raiders who began to threaten these coasts towards the end of the 2nd century AD.

Specifically excluded from this description are forts of a similar nature to those of the Saxon shore which are located elsewhere, such as on the west coast of England, or which are located along the same coastline of the main group of shore forts, but are not included in the Notitia Dignitatum, or which for structural reasons are not generally accepted as Saxon shore forts. These sites include Bitterne, Carisbrooke (Isle of Wight) and Alderney. The sites included are: Brancaster, Burgh Castle, Walton Castle (now lost), Bradwell-on-sea, Reculver, Richborough, Dover, Lympne, Pevensey, Porchester.