Bernicia was an Anglo-Saxon

Anglo-Saxons

Anglo-Saxon is a term used by historians to designate the Germanic tribes who invaded and settled the south and east of Great Britain beginning in the early 5th century AD, and the period from their creation of the English nation to the Norman conquest. The Anglo-Saxon Era denotes the period of...

 kingdom established by Anglian

Angles

The Angles is a modern English term for a Germanic people who took their name from the ancestral cultural region of Angeln, a district located in Schleswig-Holstein, Germany...

 settlers of the 6th century in what is now southeastern

Scottish Borders

The Scottish Borders is one of 32 local government council areas of Scotland. It is bordered by Dumfries and Galloway in the west, South Lanarkshire and West Lothian in the north west, City of Edinburgh, East Lothian, Midlothian to the north; and the non-metropolitan counties of Northumberland...

 Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 and North East England

North East England

North East England is one of the nine official regions of England. It covers Northumberland, County Durham, Tyne and Wear, and Teesside . The only cities in the region are Durham, Newcastle upon Tyne and Sunderland...

.

The Anglian territory of Bernicia was approximately equivalent to the modern English counties of Northumberland

Northumberland

Northumberland is the northernmost ceremonial county and a unitary district in North East England. For Eurostat purposes Northumberland is a NUTS 3 region and is one of three boroughs or unitary districts that comprise the "Northumberland and Tyne and Wear" NUTS 2 region...

 and Durham

County Durham

County Durham is a ceremonial county and unitary district in north east England. The county town is Durham. The largest settlement in the ceremonial county is the town of Darlington...

, and the former Scottish counties of Berwickshire

Berwickshire

Berwickshire or the County of Berwick is a registration county, a committee area of the Scottish Borders Council, and a lieutenancy area of Scotland, on the border with England. The town after which it is named—Berwick-upon-Tweed—was lost by Scotland to England in 1482...

 and East Lothian

East Lothian

East Lothian is one of the 32 council areas of Scotland, and a lieutenancy Area. It borders the City of Edinburgh, Scottish Borders and Midlothian. Its administrative centre is Haddington, although its largest town is Musselburgh....

, stretching from the Forth

River Forth

The River Forth , long, is the major river draining the eastern part of the central belt of Scotland.The Forth rises in Loch Ard in the Trossachs, a mountainous area some west of Stirling...

 to the Tees

River Tees

The River Tees is in Northern England. It rises on the eastern slope of Cross Fell in the North Pennines, and flows eastwards for 85 miles to reach the North Sea between Hartlepool and Redcar.-Geography:...

. In the early 7th century, it merged with its southern neighbour, Deira, to form the kingdom of Northumbria

Northumbria

Northumbria was a medieval kingdom of the Angles, in what is now Northern England and South-East Scotland, becoming subsequently an earldom in a united Anglo-Saxon kingdom of England. The name reflects the approximate southern limit to the kingdom's territory, the Humber Estuary.Northumbria was...

 and its borders subsequently expanded considerably.
Bernicia is mentioned in the 9th-century Historia Brittonum (§ 61) under the Welsh name of Berneich or Birneich and in Old Welsh poetry and elsewhere under the name of Bryneich or Brynaich.