Erir, Heremi, Heremus, Herir, Heriri, Reir
Eryri is the Welsh name for Snowdonia, a mountainous region in northwestern Wales.
Eryri is deeply connected to the Welsh culture and history. The Welsh language is spoken in the area, and the region has a rich cultural heritage that includes traditions, myths, and legends.
The name by which Geoffrey refers to Yr Wyddfa Fawr or, more usually nowadays, Mount Snowdon.
This is the area where Vortigern sought to build a fortress. It is also called Dinas Emrys. It may be related to the mountain Aravius, where Arthur slew the giant Ritho (Rhitta).
According to Tennyson, it was rumored that the infant Arthur had been found by a forester on the mountain.
Sources
Historia Brittonum | Probably Nennius, early 9th century
Brut | Layamon, late 12th century to mid-13th century
Idylls of the King | Lord Alfred Tennyson, 1859-1886