The Landsker Line is a term used for the language boundary between the largely Welsh-speaking and largely English-speaking areas in southwest Wales. The English-speaking areas, south of the Landsker line and known as Little England beyond Wales, are notable for having been English linguistically and culturally for many centuries despite being far from the border with England. The line is noted for being sharp, and for having moved only slightly over the past several centuries. A visible boundary which represents the Landsker line is Brandy Brook which runs through Newgale, the next beach North after the Brook has the Welsh name Pen-y-Cwm.
During the 11th and 12th centuries both invaders and defenders built more than fifty castles during a complex period of conflict, effectively to consolidate the line. The southernmost was Laugharne; others included Wiston, Camrose, Narberth, and Roch. These are often referred to as "frontier castles" but they were in fact set back a considerable distance from the frontier itself. In the heart of the Normanised colony, the two great fortresses were at Pembroke and Haverfordwest. There were other fortresses within the colony as well, including Manorbier, Carew and Tenby.
The Landsker has changed position many times, first moving north into the foothills of Mynydd Preseli during the military campaigns of the Early Middle Ages, and then moving southwards again in more peaceful times, as the English colonists found that farming and feudalism were difficult to maintain on cold acid soils and exposed hillsides.