The
B4518 road is a road in
Powys, central Wales, with a total length of . It begins at in
Rhayader near the junction of the
A470 road and the
A44 road and leads eventually to the A470 again at
Llanbrynmair at . En route going north from Rhayader it passes through the following settlements:
St Harmon, Pant-y-Dwr,
Tylwch,
Llanidloes (where it crosses the A470 again), Staylittle, Pont Crugnant,
Pennant,
Bont Dolgadfan,
Llan and Plas Esgair. It passes through the
Clywedog Valley and
Clywedog Reservoir, built in 1964.