n a narrow triangle between the rivers Tweed and Teviot, just before they join, is a superb site for a stronghold  known as Marchidun (Fort of the Horsemen). The haugh below the fort is large enough to grow several crops of hay and graze a breeding herd all the year round.

In the early Dark Age it was perfectly positioned to defend the Gododdin frontier with Bryneich (which later became the Angle Bernicia). It was probably the capital of Calchvyndd, the Gododdin chiefdom of the Lower Tweed. The motte is very steep and may well have been reinforced in later times with a dry moat.

The history of the chieftains of Calchvyndd is vague and complicated. After the death of Lot, in about 520AD, the High Chiefship passed to his eldest son Gawain who was committed more to religion than politics and ruled in absentium from a monastery in Wales. This was a recipe for a decentralisation of power within the Gododdin. The chieftains seem to have become increasingly autonomous. In Roman times, Bryneich had originally been part of Gododdin but had been split off around 410AD.

But in around 530AD Calchwyndd, either by inheritance or by conquest, seems to have passed back into the hands of Bryneich. In 547AD, Bamburgh, the capital of Byrneich, fell to the Angles and over the next decade Bryneich was reduced to a rump in the mountainous interior. The defeated pretender, Morcant Bulc, seems to have made his capital at Merchidun and joined the alliance of Urien of Rheged and Rydderch Hael of Strathclyde in 583AD to reclaim all the lost territory from the Angles. But before the final battle at Lindisfarne in 590AD, he arranged the assassination of Urien, hoping to claim the victory of the final battle for himself, but the coalition disintegrated. Seven years later he also murdered Urien’s heir, Owain.

The Angles returned in force and the battle of Dagsestan in 603AD almost certainly sealed Morcant’s fate and that of Calchvyndd. Merchidun passed into Angle hands and became Hrocs burgh (Roxburgh). It continued to be important during the Angle/Northumbrian period and in mediaeval times grew into the third most important city in Scotland. It is where urban life in Scotland began with four churches and a royal mint. But being close to the English frontier, it was constantly subject to surprise attack and, after an exploding cannon killed James II in 1460AD, the Castle was dismantled and the city was burned by the Scots. All that remains of the great mediaeval city are a few chunks of the city walls.