The fort was shaped rather like a playing card with defences of earth and timber, symmetrically placed gates and streets of timber-framed buildings.
Roedd siâp y gaer yn ddigon tebyg i gerdyn chwarae gydag amddiffynfeydd o bridd a phren, giatiau wedi'u gosod yn gymesur a strydoedd o adeiladau ffrâm bren.