A moat is a broad water-filled ditch that surrounds a central platform or ‘island’ where a house usually placed. Although inspired by castles, the defensive banks and walls of true castles are characteristically absent on moated sites. The possession of a defended residence was closely linked in the medieval mind with concepts of lordship and social status: great lords had their castles, lesser members of the free classes (knights, esquires, clergy and freehold farmers) had, where conditions were suitable, moated houses.

A social hierarchy is apparent in the size of moats: those that are an acre or more in extent tend to be manorial (e.g. Brockley Hall) or monastic (e.g. Flixton Priory). Moats of about half an acre in size are much more likely to be associated with parsonages (e.g. The Old Rectory, Whatfield) or farms that are ancient free tenements (e.g. Oak Tree Farm, Hitcham).

The majority of moats function like ponds, relying on an impervious base or lining, though some are connected to water-courses. Suffolk has over 850 moats and vies with Essex for the distinction of having the largest number in England. They occur in a broad diagonal band across Suffolk in a distribution pattern that is closely related to the natural occurrence of water-retentive clay soils (see glacial till).

The earliest moated sites date from between about 1150 and 1200. They continued to be built until about 1550, but the majority seem to belong to the period 1200-1325.

Barns and other agricultural buildings are rarely sited on the same moated platform as the house, they are usually situated just outside, flanking the approach to the entrance. Sometimes they are contained within their own moated or ditched enclosure. Moats can also surround banqueting houses or ‘gloriets’ (Letheringham Lodge), deer park lodges (Rishangles Lodge, Thorndon), gardens (Shelley Hall), fishponds (Balsdon Hall, Acton) and dovecotes (Otley Hall).