Gwenllian ferch Gruffydd (1097 – 1136) was the wife of Gruffydd ap Rhys, Prince of Deheubarth in south west Wales and the daughter of Gruffudd ap Cynan, Prince of Gwynedd. After her father-in-law Rhys ap Tewdwr was killed in battle against the invading Normans at Brecon in 1093, the way was left open for the conquest of Deheubarth. Despite the efforts of her husband to restore his kingdom, by the 1130s the only territory left under his control was the commote of Caeo in Cantref Mawr (North east Carmarthenshire).

The civil war in England between Stephen and Matilda following the death of King Henry 1 was the opportunity for the Welsh to rise. By 1136 Gruffydd ap Rhys was in Gwynedd raising more troops. In Kidwelly, the Norman motte and bailey castle (not the later stone castle,) was in the process of being transferred from the Bishop of Salisbury into the possession of Maurice de Londres, a much disliked knight. Fearing a change for the worse, this prompted Gwenllian to act quickly and before her husband’s return from the north. Moving out of their stronghold in Caeo, her army probably crossed the Tywi either at Llandeilo or Dryslwyn and approached Kidwelly from the north east and gave battle against de Londres’ greater force about a mile from the castle. So confident was she of victory that she had taken two of her sons with her into battle.The Norman army had the advantage of being on slightly raised ground, now occupied by a farm known as Maes Gwenllian. Gerald Cambrensis writing 50 years after the event states that Gwenllian’s army was defeated and Morgan her son killed. Gwenllian herself and another son Maelgwyn were captured and executed in front of her defeated troops.

Although Gwenllian’s actions were a failure, with terrible consequences for her and her sons, it did stimulate the country to rise and put back Norman rule by almost 150 years. Her youngest son was The Lord Rhys who succeeded in reuniting the Kingdom of Deheubarth.