Hatterrall Hill (Welsh: Mynydd Y Gader) is a rounded peak in the Black Mountains which sits on the Wales-England border, partly in Monmouthshire, Wales and partly in Herefordshire, England. Its summit at 531m is the high point of a peaty plateau which falls away steeply on all sides. Broad ridges run to the north, the southeast and southwest. To the north the ridge (known as Hatterrall Ridge) dips to a col at around 485m elevation before rising gradually over several kilometres towards Crib y Garth / Black Hill and Hay Bluff. The ridge to the southwest ends abruptly at the sheer cliff known as the Darren below which is a considerable landslipped area extending south to the hamlet of Cwmyoy with its mis-shapen church. The Welsh part of the hill falls within the Brecon Beacons National Park.