Eidyn

Eidyn is the Brythonic name historically used for the area around the present-day city of Edinburgh, in southeastern Scotland. The term is best known from late antique sources that describe a fortress at Din Eidyn on Castle Rock overlooking the Firth of Forth. The name Din Eidyn is usually understood as "the fortress of Eidyn," with Eidyn serving as the personal or tribal name associated with the site.

Din Eidyn formed the heart of the Gododdin, a Brythonic kingdom that occupied parts of what is now the Scottish Borders and the eastern Lothians. The stronghold is celebrated in early Welsh poetry, notably Y Gododdin, which presents Din Eidyn as the seat of the Brittonic polity and a center of warrior culture.

With the expansion of Anglo-Saxon powers in the later centuries of late antiquity and early medieval times, the Eidyn region came under increasing Northumbrian and then broader Scottish influence. The fortress remained a key site in regional power struggles and, by the High Middle Ages, Edinburgh began to emerge as the principal settlement in the area. The name Edinburgh itself is ultimately derived from Din Eidyn, through subsequent linguistic changes that produced the modern toponym.

Today, Eidyn is used mainly in scholarly and historical contexts to designate the historic Brythonic territory around Edinburgh. The term helps scholars distinguish the ancient region from later medieval political entities and from the modern city that grew from its fortified core.