What is "cemais"

thumb|200px|right|Ancient Dyfed showing the cantref of Cemais and its commotes thumb|200px|right|Pembrokeshire showing the hundred of Cemais

Cemais (sometimes spelled Kemes after one of the several variations found in Medieval orthography) was a cantref of Dyfed, and now part of Pembrokeshire, Wales. It occupied the coastal area between the Teifi estuary and Fishguard, and the northern and southern slopes of the Preseli Hills, and had an area of about 359 km. The Afon Nyfer divided it into two commotes: Is Nyfer to the north and Uwch Nyfer to the south.

It was occupied by the Normans in the 12th century, and made part of the March, but remained exclusively Welsh-speaking. The initial power-base of the Marcher Lordship was at Nevern, but was soon moved to the borough of Newport, which remains the seat of the Lords of Cemais in modern times. Nevern was the ecclesiastical centre of the cantref, and may have been the seat of a bishop. George Owen was Lord of Cemais 1574-1613 and produced a detailed parish-by-parish description of the Lordship in his second book.

The Hundred of Cemais was created from the cantref at the time of the Acts of Union of 1535-1542, by transferring the parish of Llantood to Cilgerran hundred and adding a small area of Cantref Gwarthaf cantref.

Cemais was one of the three medieval cantrefs on the island of Anglesey, north Wales, in the Kingdom of Gwynedd. It lay on the northern side of the island on the Irish Sea.

The cantref consisted of the two cwmwds of Talybolion and Twrcelyn.