Eidyn was the region around modern Edinburgh in Britain's sub-Roman and early medieval periods, approximately the 5th–7th centuries. It centred on the stronghold of Din Eidyn, thought to have been at Castle Rock, now the site of Edinburgh Castle, and apparently included much of the area below the Firth of Forth. 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.

Edinburgh is the capital city of Scotland and one of its 32 council areas. The city is located in south-east Scotland, and is bounded to the north by the Firth of Forth estuary and to the south by the Pentland Hills. Edinburgh had a population of 506,520 in mid-2020, making it the second-most populous city in Scotland and the seventh-most populous in the United Kingdom. The wider metropolitan area has a population of 912,490.