The Cadw sign at the entrance to Castell Bryn-Gwyn says,
The nature of this site is uncertain although it may have originally been a religious sanctuary. The earliest bank and ditch belong to the end of the neolithic period (2500-2000 BC) but the site was re-occupied and fortified in Roman times and later.
On the ground it’s easy to see why everyone is so cagey about defining this site.