Glywysing was, from the sub-Roman period to the Early Middle Ages, a petty kingdom in south-east Wales. Its people were descended from the Iron Age tribe of the Silures, and frequently in union with Gwent, merging to form Morgannwg. Name and early history 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 (modern Gloucester). 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. However historians and researchers claim that this is highly inaccurate as Cydweli and Gwyr were highly likely to be independent cantrefs within the Ystrad Tywi ruled by local warlords and were not under any ruling Kingdom until Dyfed sometime around the late 5th to early 6th Century. Location The borders changed over time, but it is generally thought that its lands originally lay between the Afon Llwyd and either the River Towy, the River Loughor, or the River Neath.At times they expanded eastwards in union with both Gwent and Ergyng. The Gower had either returned or was inherited from Dyfed 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 (fl. ) until the end of the reign of his descendant Ithel (d. c. 745), and later again under King Morgan the Old (r. 942-74), 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