Perfeddwlad, that is the 'middle country', was a name adopted during the twelfth century for the territories in north-east Wales lying between the rivers Conway and Dee, and comprised the cantrefi of Rhos, Rhufoniog, Dyffryn Clwyd and Tegeingl.
It was known as the 'middle country' because it was situated between the two kingdoms of Gwynedd and Powys and was therefore the subject of dispute between those two kingdoms. It was also situated between Gwynedd and the realm of England to the east, and therefore contested by those two kingdoms, particularly as the Norman kings of England sought to expand their control over Wales.
Despite the fact that the eastern half of the Perfeddwlad, to the east of the river Clwyd came under Norman influence in the late eleventh century, (many settlements were listed in the Doomsday Book of 1086), it was also known known as Gwynedd Is Conwy, that is 'Gwynedd below the river Conway' when under the sway of Gwynedd as during the reign of Llywelyn Fawr.
Following the death of Llywelyn Fawr the Perfeddwlad was conquered by Henry III in the 1240s but retaken for Gwynedd by Llywelyn ap Gruffudd in the 1260s. It was retaken once more by Edward I in the 1270's who kept the two northern cantrefs of Rhos and Tegeingl for the crown but ceded Rhufoniog and Dyffryn Clwyd to Dafydd,Llywelyn's brother who sided with Edward.
Following Edward's final victory in the years 1282-1283 and the
consequent Statute of Rhuddlan in 1284, Rhos and Rhufoniog were combined to form the new lordship of Denbigh and conferred upon Henry de Lacy, earl of Lincoln; Dyffryn Clwyd becoming the lordship of Ruthin and granted to Reginald de Grey; and Tegeingl became the lordship of Englefield and the main body of the proto-county of Flint under the aegis of the palatinate of Chester.
Sourced from the Clwyd-Powys Archaeological Trust website at http://www.cpat.org.uk/index.htm and the Market House Books Dictionary of British History at http://www.xrefer.com/entry/363213