It was the most important district of the Brittonic kingdom of Gododdin, and a significant power in the Hen Ogledd, or Old North, the Brittonic-speaking area of what is now southern Scotland and northern England.
The site of Din Eidyn has been nearly continuously occupied since the Bronze Age, serving as a stronghold of the Votadini during the Roman era and later the principal centre of their successors, the Gododdin kingdom.
Eidyn's importance to the Hen Ogledd is reflected in the medieval poem Y Gododdin, which concerns a war band that gathered there for a raid around AD 600.
[12] Around 143, Emperor Antoninus Pius commenced the Antonine Wall north of the Votadini and what would become Eidyn, with its eastern terminus likely at Carriden.
The work relates that a force of 300 distinguished warriors from across the Brittonic world assembled at Din Eidyn for a raid on Catraeth (probably Catterick) around AD 600.
[16] The poem's dense language and convoluted history make it difficult to interpret the historical events underlying the work.
According to Ifor Williams' interpretation, the warriors were summoned by Mynydawc Eidyn, perhaps a Gododdin ruler, to attack the Angles holding Catraeth.
[16] Later scholars such as John Koch and Graham Isaac have challenged elements of this interpretation, and read Mynydawc as a place name referring to a mountain, not as a ruler.
The Annals of Clonmacnoise indicate that Æthelstan of England "spoiled the kingdom of Edinburgh" in 934, suggesting a fortification of some note existed at that time.
[20] Among these, archaeologists generally identify the Castle Rock site as Din Eidyn, as the evidence indicates it was an important centre continuously from Roman times into the Middle Ages.
[18][19][21] Archaeological evidence suggests Castle Rock has been inhabited since the Bronze Age, possibly making it the oldest site in Scotland that has been nearly continuously occupied.
Its easily defended location appears to have given it an advantage over other nearby sites such as Arthur's Seat, where settlement was evidently unstable and not continuous.
[24] In the Roman era, the site supported a prosperous settlement that likely included a hillfort, perhaps featuring a broch (roundhouse).
[25] In this period, Castle Rock was apparently one of the major centres of the Votadini, though it was dwarfed by Traprain Law, which was ten times larger.
It also mentions Bedwyr (the Sir Bedivere of later tradition) sparring with Garwlwyd ("Rough-Grey"), evidently one of the monsters, at the "shores of Tryfrwyd".