As mentioned above, the frontier moved between 1600 and today. Historic data on personal names also show that it also moved between 1200 and 1600. Attempts to set up a number of Norman/English “planned villages” (e.g. Letterston and New Moat) were made north of the current frontier in the mediæval period. These subsequently failed, and were re-occupied by Welsh speakers in the post Black Death period. In more modern times, the enclosure of commons allowed a substantial southward spread of Welsh speakers, particularly in Carmarthenshire. These are quite rare examples of Welsh-speaking areas expanding at the expense of English-speaking areas; in the central part of Pembrokeshire the shift of the Landsker southwards between 1600 and 1900 was in excess of 10 km.