The name
Nidum was well attested by the 19th century. It is included in the
Antonine Itinerary, a Roman period register of forts and distances along various routes around the Roman world.
Iter 12 of the Britannia Itineraries, adjusting for errors in the medieval transcriptions, places Nidum 14
miles east of Leucarum (modern day
Loughor), and 27 miles west of Bomio (an unknown fort, possibly
Cowbridge). Bomio is itself listed as being 28 miles from
Isca Augusta (modern day
Caerleon). In the west the road is believed to have continued a further 23 miles from Leucarum to
Moridunum, the fort and walled town at
Carmarthen. The clear similarity of Nidum and the Welsh
Nedd, helped confirm that a Roman Fort must have been built in the Neath area. Often identifiable lines of Roman roads have led straight to fort locations. However no evidence remains of the Roman roads leaving Neath either to the east or west. The routes are presumed to have existed however and are given the
RCAHMW numbers 'RR60c' (to the east) and RR60d (to the west). These routes are classed as 'predicted' in the viscinity of Neath, so were no help in locating the fort of Nidum. To the north-east another unknown route leads to the well-defined Roman road designated RR622. It runs to
Y Gaer, (Brecon), via the 'Coelbren Fort' at
Banwen, which is north-east of Nidum. This is one of various Roman roads in Wales traditionally known as the
Sarn Helen. ==Archaeological evidence==