Emlyn was one of the seven cantrefi of Dyfed, an ancient district of Wales. It became part of Deheubarth in around 950. It consisted of the northern part of Dyfed bordering on the River Teifi. Its southern boundary followed the ridge of the line of hills separating the Teifi valley from the valleys of the Tâf and Tywi. The cantref was made part of the Norman March in the 12th century, and many castles were built, including those of Cilgerran and Newcastle Emlyn. Nevertheless, the area remained Welsh speaking, as it continues today.