Yr Hen Ogledd is a Welsh term meaning 'The Old North' and referring to the sub-Roman Brythonic kingdoms of what is now northern England (including Cumbria) and southern Scotland. Cumbric, a dialect of Brythonic closely related to Old Welsh, was the language of the Men of the North (Gwŷr y Gogledd in Welsh).
These kingdoms flourished during the 5th, 6th and 7th centuries in the area south of the Pictish lands. The people of these nations, and most often their kings, are referred to as the Gwŷr y Gogledd or 'Men of the North'. A series of Old Welsh pedigrees under this title appears to show the descent of many of these monarchs. Almost all of them begin with a common ancestor, Coel Hen ("Coel", from the Roman "Coelistius"), and John Morris has suggested that this man was the last Roman Dux Britanniarum with military control over all of the north of Romanised Britain at the time of the Roman withdrawal. After his death, his large and powerful 'realm' would thus have been divided, as was the custom, between his sons or, more probably, subordinate commanders, to be ruled by them and their successors.
The other source Morris gives for the northern dynasties is a group of Roman citizens installed, according to tradition by Magnus Maximus (Maxen Wledig), as "praefecti gentium" over the "barbarian" tribes in the north between the Walls (Hadrian's Wall and Antonine Wall): Quintilius son of Clemens at Alt Clut, Paternus ap Tacitus among the northern Votadini at Din Paladur (Traprain Law), Catellius Decianus among the southern Votadini at Din Gefron (Yeavering Bell), Maximus’ son Antonius Donatus Gregorius (son of Magnus Maximus) among the Novantae at first, but later in Demetia in Wales. Cunedda, grandson of Paternus, later migrated to North Wales, where he became the patriarch of the dynasty that ultimately came to rule all of Wales. The descendants of Catellius Decianus migrated north to Traprain Law at that time, and when the dynasty of Quintilius son of Clemens died out, they again transferred their seat, to Alt Clut, where their dynasty intermarried with those of the Picts of Fortriu and various branches of the Dal Riata.
The names of some of these kingdoms and possible sub-kingdoms have been lost to history, but the ones that are known to us, sometimes thanks to a single reference in an early Welsh text, are:
These states were all extinguished or brought under other kingdoms following successive attacks or diplomatic takeovers from the 6th Century onwards by the Angles of Bernicia and Deira (which merged to become Northumbria), and by the Kingdom of the Picts which also absorbed the Kingdom of Dal Riata, then united the two realms as the Kingdom of Alba.