Ringfort

A ringfort, ring fort or ring fortress is a fortified settlement. Ring forts were made to protect villages, mostly in the Middle Ages. In Ireland where many such forts can be found, they are also known as ráth, caiseal, cathair and dún in the early Irish sources.
A "ráth" (anglicised rath), was made of earth, "caiseal" (northwestern Ireland, anglicised cashel) and "cathair" (southwestern Ireland) were built of stone. A "dun" is a more prestigious site, the seat of some kind of ruler, the term is applied to promontory forts as well.