Although the exact date of the hillfort's construction is unknown, it is presumed to predate
the Roman conquest of Wales and the site "was fortified with no mean engineering skill and knowledge." Surface finds and partial excavations carried out since the early 1800s have uncovered pottery of Roman origin and many coins which suggest the site was occupied "by a large native population, say, from A.D. 100 to 400." A gold coin of
Nero's time was found nearby at Llanrhydd in 1823. According to later legend recorded in the
Historia Brittonum the "iniquitous and tyrannical" king
Benlli (after whom the mountain was named) probably lived there c. 450. He was admonished for opposing
Saint Germanus, and he and his castle were "consumed by fire from heaven", so the legend goes. There are the remains of strong ramparts on all sides, with an entrance at the west end. In the south-west quarter of the fort enclosure are about two dozen hut platforms; there is a spring close to the centre. File:Stone cairn at the summit of Foel Fenlii.jpg|Cairn at the summit ==See also==