Penychen was one of three cantrefi that made up the kingdom of Glywysing, lying between the rivers Taff and Thaw, the other two being Gwynllwg and Gorfynydd.
According to tradition, these cantrefi were created on the death of Glywys (c.480 AD), the first king of Glywysing, when the kingdom was divided between his three sons: Pawl, Gwynllyw and Mechwyn.
But our knowledge of the early history of the kingdom is very uncertain, being mainly sourced from medieval documents and traditional pedigrees.
After the Norman conquest of South Wales, the southern parts of Penychen, on the Bristol Channel, came under the direct rule of the Norman Marcher Lords and their descendants, but the rest (the commotes of Rhondda Valley and Miskin) remained under the rule of local Welsh lords, who paid homage to the powerful Norman lords but still retained a degree of independence, which they were very ready to defend.
Penychen lay between Senghenydd and Gwrinydd in South Wales;[2] it contained the areas which today are the county borough of Rhondda Cynon Taff, the majority of the Vale of Glamorgan and the west of Cardiff.