Nidum (or NIDVM) is a Roman fort found near the town of Neath, in Wales. An Auxiliary fort first built in around 74AD from earth banks and wooden structures, it underwent a reduction in size from 3.3 to 2.3 ha soon afterwards. It may have been garrisoned by perhaps 500 Auxiliary troops. It was abandoned in around 125AD, but re-occupied around 140AD when it was rebuilt in stone.