Castell-Mawr was described by Ieuan Hughes in TCAS 1926, p. 26, as; 'Originally a circular camp enclosed by a single ring of defence it is now under cultivation and almost obliterated. A protracted period of search along the furrows over this site and in the fields bought no results.'. The note shows the fort has been well ploughed for a century or more.

Aerial photography by RCAHMW during several dry summers during the 1980s and 1990s, has revealed parchmarks showing a complex site to survive below ground. The parchmarks show the stonework of a main rampart (presently preserved as an earthwork on the ground) encircling the promontory, with a deep outer ditch, and then further lines of two or three ditches (on the north side). Inside the main fort is the parchmark of a thinner stone wall enclosing a smaller space, which may represent an early phase in the fort's development.

A field visit showed very little surface topography to survive on site through repeated ploughing. Traces of low (c 30-50cm) rampart were traceable on the north and northeast sides, while only a terrace survives on the other. Traces of scarp slope can be seen through a hedge on west side above Allt Fawr but this is obscured by vegetation and badger sets.

Taken together, Castell Mawr was clearly a fort occupied and rebuilt through a number of different phases, of which substantial below-ground remains still survive.

Visited T Driver, RCAHMW & A Fleming, UW Lampeter, 15th March 2002.