David’s confidence was growing, as Stephen faced rebellion by Matilda’s supporters in the south, and in the summer of 1138 he invaded once more. This time there were two forces. One advanced along the west coast route, defeating an English army at Clitheroe (Lancashire, 1138) and the marching south on the east coast to Newcastle.

It was then in July that Eustace fitz John, who held the important castles of Alnwick and Malton, defected to Matilda’s cause and joined David in the north. Bolstered by this English support the Scots called up further forces, turning this into a major invasion, and besieged other places in the north, including the castle of Wark. It is claimed that in all he brought together a force of 25,000 men, although medieval sources frequently inflate troop numbers substantially.

As David’s army marched south they are said to have conducted systematic looting, including capturing peasants to take into Scotland as slaves. This encouraged a decisive response from the northern English barons. King Stephen was campaigning in the south of England and so the responsibility for organising the defence fell upon his lieutenant in the north, Archbishop Thurstan of York. He was then aged about 70 and, although his skills were as an administrator not as a field commander, he successfully promoted the action as a holy crusade against the Scots.

In the first week of August he began to assemble an army at York, with local levies and other forces instructed to assemble further to the north at Thirsk. On about the 14th August the army marched north from York. Thurstan was too old and infirm to travel north himself and so he sent his deputy, the Bishop of Orkney, to accompany the army. The general rendezvous of all the forces took place at Thirsk.

When moving an army the best roads would be chosen so that the force could be moved as quickly as possible. There is much we do not yet know about the road system of 12th century England, but some Roman roads were certainly still in use and Thirsk lay on one that ran north from York, while the Scottish forces seem to have been using the Great North Road in their advance south. At Northallerton these two route ran close to each other.

There were two major Roman roads running north through Yorkshire. One, later broadly followed by the Great North Road, was in the west, between the Pennines and the marshes of the Vale of York. The other lay further the east, between the marshes on the west and the upland of North York Moors on the east. It is uncertain the degree to which the 12th century road system still followed the Roman, but Thirsk lay on the latter and within striking distance of the northern border of Yorkshire. A little to the north, near Northallerton the two routes approached close to each other and by the 12th century may even have joined before they crossed the Tees. If David marched south then his army would have to take one or other of these roads. Assembling the English army at Thirsk placed them in a position to counter the Scots whichever route they took through this relatively narrow corridor of lowland between Pennines, marsh and Moor, which was the only realistic route into the heart of Yorkshire.

As usual in early medieval warfare attempts were first made to try to settle the question by negotiation. Bernard de Balliol and Robert of Bruce, who both held lands in Scotland and knew David, were dispatched to negotiate with the Scots. They presented terms for a truce that had been sent by Stephen, who offered to recognise David’s son Henry as Earl of Huntingdon and Northumbria. But David rejected the terms and on the 21st August the Scottish army crossed the river Tees.

It would appear that the Scots advanced along the Great North Road, already recorded in 1250 as the major route to the north, which ran south through Northallerton, just 10 miles south of the Tees. When this was reported by their scouts, early on the morning of the 22nd August, the English army marched north to counter the Scots. They bypassed Northallerton, perhaps using the route through Brampton village. Although now just a lane, this may have been a significant early medieval route which joins the Great North Road at the northern edge of the battlefield, two miles north of Northallerton.