Bryn Arw is a hill in the Black Mountains of the Brecon Beacons National Park in Monmouthshire, south Wales. It lies 4 km north of the town of Abergavenny and 1.5 miles west of the village of Llanvihangel Crucorney. Its summit at 384m above sea level is the more northerly of two tops which lie on the crest of a slightly arcuate north-south ridge which drops away to the south at first gently and then sharply. The hill is isolated from the main mass of the range by the valleys of Cwm Coed-y-cerig to the north and by Cwm Brynarw to the west. It is a Marilyn.