Caerphilly
county borough, southeastern Wales. The area west of the River Rhymney forms part of the historic county of Glamorgan (Morgannwg), and the area east of the river belongs to the historic county of Monmouthshire (Sir Fynwy). Caerphilly county borough extends from the edge of Brecon Beacons National Park in the north to the outskirts of the city of Cardiff in the south and includes several deep valleys separated by wooded hills
Learn more about Caerphilly with a free trial on Britannica.com.