With a summit at an elevation of 511 metres (1,677 ft), it is the second highest peak of the Clwydian Range.

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.

[2] 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.