Истрад-Тиви
In medieval times Ystrad Tywi was divided into three cantrefi: Cantref Mawr on the north bank; Cantref Bychan and Cantref Eginawc on the south bank of the river. Eginawc (comprising the commotes of Gŵyr, Carnywyllawn, and Kidwelly) was lost to the Normans in the 11th century, and for the rest of the Middle Ages only the other two cantrefi formed Ystrad Tywi.