One explanation is the legend of the Twelve Knights of Glamorgan, which dates from the 16th century, in which the Welsh Prince Iestyn ap Gwrgan (Jestin), prince or Lord of Glamorgan, supposedly called in the assistance of Robert Fitzhamon.
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Coity Castle in Glamorgan, Wales is a Norman castle built by Sir Payn "the Demon" de Turberville (fl. 1126), one of the legendary Twelve Knights of Glamorgan supposed to have conquered Glamorgan under the leadership of Robert FitzHamon (d.1107), Lord of Gloucester.
Neath Abbey was established in 1129 AD when Sir Richard de Granville, one of the Twelve Knights of Glamorgan, gave 8,000 acres (32 km²) of his estate in Glamorgan, Wales to Savigniac monks from western Normandy.