Battle of Roslin
Background
After the Battle of Falkirk in 1298, the English occupied Scotland and were governed by Sir John de Segrave on behalf of King Edward I of England. A truce between England and Scotland ended on November 30th, 1302, and insurrection was in the air. Edward started to prepare for another invasion of Scotland and ordered John de Segrave to organize scouting parties across Scotland as far north as Kirkintilloch, before organizing an army.

De Segrave mustered a force of 30,000 troops at Wark, on the River Tweed, in early 1303, which was split into three divisions of 10,000 each as they moved north into Scotland.
The Scots were not sitting idly by; they knew a force was coming, and John Comyn, Lord of Badenoch, and Simon Fraser prepared a Scottish army to confront the English.
As the English advanced into Scotland, the three divisions began to distance themselves from each other and camped several miles apart from each other near Roslin, just south of Edinburgh.
As the English rested in their camps at night, John Comyn and Simon Fraser marched through the night with a force of 8,000 men.
Battle
In the early morning hours of February 24th, 1303, the Scottish forces led by John Comyn and Simon Fraser attacked the first camp of the English under cover of darkness, taking them completely by surprise near the River Esk. The English camp quickly fell, and many troops were taken captive, including John de Segrave, to be ransomed later. Soldiers of no ransom value were put to the sword.
Some surviving English troops from the skirmish managed to escape the battlefield and reached the second camp, and informed them of what had happened. Having heard what had transpired, the second English army, led by Ralph de Confrey, mustered and headed towards the Scottish army, who now realized a second English army was headed towards them and prepared for a pitched battle. Most of the English that had been taken prisoner to be ransomed were now killed by the Scots so that they could focus all resources on the arriving forces.

Both armies clashed in open battle. After a few hours of intense fighting and heavy losses on both sides, the English ranks broke and fled. The Scots were victorious! But this was shoprt lived
The Scots soon realized there was a third English army, led by Robert Neville, now cresting over the hillside towards them. Realizing a retreat would have been difficult, John Comyn rode out in front of his army and gave a rallying speech, reminding his troops of their desire for freedom and that their ancestors were watching their exploits. The Scots, although tired and depleted, were rejuvenated and aligned for battle.
The final clash again lasted for hours. With leadership from Comyn and the tactical advantage of an ambush from the higher ground of the valley, the Scots defeated the English, with only 2,000 - 3,000 of the 10,000 English surviving back to England.
Aftermath
John de Segrave survived the battle and was ransomed for a heavy amount on his head. He would play a larger role in the Scottish War of Independence. De Segrave's paymaster, Ralph Manton, was killed during the fighting.
The Battle of Roslin was a significant victory for Scotland over the English, but the regime of Robert the Bruce would downplay it, as John Comyn was a bitter rival of the Bruce. Thus, the Battle of Roslin was never quite recognized in history like other major battles, such as those at Stirling Bridge or Bannockburn.
Robert the Bruce would murder John Comyn at the altar of the Church of the Greyfriars at Dumfries, a few years later in 1306.
The loss was a setback for the English, but since the army of 10,000 was mainly made up of mercenaries and Scots loyal to Edward I, Edward would still be able to rally an even larger army in England. The First War of Scottish Independence would continue.
A monument cairn was erected at the site of the battle at the end of the 20th century by the Roslin Heritage Society.