Who commanded the armies?
From the North:
Two armies combined to attack the northern part of Northumbria. One was led by Malcolm II, King of Alba (the Highlands); the other led by Owen the Bald of Strathclyde (then including Strathclyde and the Lake District). The two armies merged near Galashiels before proceeding eastwards to confront an army commanded by the Earl of Northumbria.
There is opinion that Malcolm II and Owen the Bald were related. Owen died in 1018, perhaps killed at the Battle of Carham, and Strathclyde was incorporated into the realm of Malcolm II. If the two were related it would ease the combining of the two kingdoms into one and be a significant step in the emergence of Scotland as we know today.
From the South:
There is a difference of opinion as to who was Earl of Northumbria in 1018 and therefore commander of the Northumbrian army. Uhtred is the usual choice, but of course this is not possible if he had been killed in 1016. The alternative candidate is Uhtred's brother, Eadwulf Cudel. Eadwulf gained the addition Cudel, meaning cowardly, because he is accused by some of giving Lothian to the Scots because he was in fear for his life.
The Northumbrian army was raised from the land between the rivers Tees and Tweed, suggesting that Lothian had already been ceded to the Scots.
Did the Battle of Carham fix the Border?
When Northumbria was at the height of its power, Carham was merely a place on a river in the middle of the kingdom. Raids by the Scots gradually diminished the security of the northern part of Northumbria. In 1006 Malcolm raided much further south, but was defeated at Durham by Uhtred, Earl of Northumbria and he retreated back to the Highlands. Northumbria was also being severely harassed in the south by the Danes and was consolidating its power in the central area from Tees to Tweed.
The River Tweed became a defensive line for Northumbrians and Scots, and although there were incursions over this line for many years to come, the Battle of Carham in 1018 was the defining moment in the process of fixing the Border.
The Border was not fixed in law until the Teaty of York in 1237 - although subsequently, the town of Berwick changed hands many times.
The weapons and tactics of the times
The weapons of war in early medieval times were very basic. Sword, battle axe, knife and spear were the favoured hand weapons, with the war bow for more distant death and destruction. Body armour consisted of keather jerkin and chain mail shirt, all topped with a steel helmet. A heavy steel rimmed round wooden shield was used both as a defensive and offensive weapon.
Battles were short, hard, vicious, brutal and bloody affairs. Armies were small compared to later years and were raised from local manpower; at Carham the army was raised from the area between the rivers Tees and Tweed. A commonly used tactic was the shield wall when shields were locked together as a barrier to the attacking force. Cavalry was used, but usually in limited numbers.