Glywysing is said to be named after Glywys, a real or legendary early monarch, whose name may continue that of the Romano-British *Glevenses, the territory and citizens of Glevum. According to 12th-century sources, after the death of Glywys, the kingdom was divided into seven cantrefs named for his sons: Cydweli, Gwyr, Margam, Penychen, Gwynllwg, Gorfynydd, and another. These were typically ruled together by the head of the family and sometimes treated as appenage subkingdoms.
Location
The borders changed over time, but it is generally thought that its lands originally lay between the Afon Llwyd and the River Towy. At times they expanded eastwards in union with both Gwent and Ergyng. Some time before the early 8th century, Cydweli and Gwyr were lost to Dyfed, although the Gower had returned to Glywysing by 928 prior to the reign of King Morgan the Old. Today the area of Glywysing is known as Glamorgan.
Morgannwg
First under King Morgan the Generous until the end of the reign of his descendant Ithel, and later again under King Morgan the Old, the kingdom merged with Gwent and changed its name to Morgannwg or Gwlad Morgan in honour of the Morgan Kings. During such unions Glywysing and Gwent seem to have been together or occasional sub-kingdoms or principalities of the Kingdom of Morgannwg. After the death of Morgan the Old, Gwent and Glywysing were separated again from 974 to 1055, but Glywysing alone was often referred to as Morgannwg. Both areas were conquered by Gruffydd ap Llywelyn in about 1055, subsequently King of Wales, but on Gruffydd's death in 1063, Glywysing was regained by the native lineage under Caradog ap Gruffudd. Morgannwg, the union between Gwent and Glywysing, was reconstituted. How this occurred is unclear; possibly the Kings of Glywysing were also Kings of Morgannwg and the Kings of Gwent were semi-independent under-Kings, or vice versa.
With Gwent increasingly overrun by the Norman conquest of Wales, the last native King of Morgannwyg & Glywysing was Iestyn ap Gwrgan, who was subsequently deposed by Robert Fitzhamon. Iestyn's sons became Lords of Afan, while Owain ap Caradogap Gruffudd contented himself with Gwynllwg and founded the line of the Lords of Caerleon. The name Morgannwg is still used in Wales for the former Marcher Lordship and county of Glamorgan and its successor counties.
