Bruce's army, like William Wallace's before him, was chiefly composed of infantry armed with 18-foot long pikes. It was divided into three main (infantry) battalions, and a fourth larger battalion commanded by the king himself serving as the reserve unit. The second battalion was commanded by Thomas Randolph, 1st Earl of Moray. The third was led by Edward Bruce, the king's brother. The fourth division was commanded by Sir James Douglas and his cousin Walter the Steward. The light cavalry of 500 strong was commanded by Robert Keith, Marischal of Scotland. Each infantry division formed into a Schiltron formation. Each man carried the pike upright and the outside ranks would lower theirs to form a lethal wall of sharp metal points. The schiltron could withstand an attack by knights on horses. But Bruce also trained them to attack.
Bruce's army had been gathering in the Tor Wood, an area that gave good natural cover. Bruce then moved his army just to the north to the New Park. This was more heavily wooded area where his movements could be concealed. It could also provide cover for a retreat if needed. The Scottish king chose his ground very carefully. The Bannock burn (or stream), which the English army had to cross on the way to Stirling was a natural obstacle. Parts of it were too deep for infantry or cavalry to cross. The area was also covered with marshy boggy ground difficult to ride over. Sir Thomas Gray called it "an evil, deep, wet marsh". On the east side was a sharp drop of 50 feet or more. The trees of the New Park were on the west side. Also, pits were dug as traps to break a cavalry charge. No matter which way the English cavalry tried to go they would be tangled up and be easy targets for the Scottish infantry.
The only approach was over the old road from Falkirk to Sterling. This route was the only solid ground on which heavy cavalry could be moved.
Bruce's three main divisions numbered about 1,000 strong each. His own reserve division was at double strength or about 2,000 strong. The Marischal's light cavalry was about 500 horse and there was a small group of archers. Together the Scottish army numbered between 5,000 and 6,000 men. This was about one-fourth the size of Edward's force.
The English army reached Tor Wood on June 23rd and stopped. They were met by Sir Philip Mowbray, the English commander of Stirling Castle. He told the king there was no need for battle. Edward had fulfilled his obligation to relieve the castle by coming within three leagues. Also he had seen Bruce's preparations and warned of trying to attack the Scots with heavy cavalry. Like Edward II and his commanders, Mowbray thought the Scots would retreat when they saw the size of Edward's great army. The vanguard of Edward's forces under Gloucester had already crossed the ford over the Bannockburn towards the Scottish lines. An English knight Henry de Bohun was riding ahead of his companions when he caught sight of
the Scottish king inspecting some of his lines. De Bohun lowered his lance and charged. Robert the Bruce was mounted on a small palfrey and armed with a battle-axe He could have simply moved behind his men and let them repel the charging warhorse and rider. Instead he turned his horse and rode towards de Bohun. At the last moment Bruce swerved his horse to one side, missing de Bohun's lance. He then rose in his stirrups and brought down his axe with such force he cut through de Bohun's helmet killing him instantly. There was a stunned silence by both armies then a great cheer rose among the Scottish soldiers. Then the highlanders of Bruce's own division charged the English cavalry who were still lining up. The horses of the Earl of Gloucester and several others stumbled as they fell into the hidden pits. The earl was rescued but the English cavalry fled from the charging Scots. King Robert stopped their charge and they returned to their lines. This showed how well-disciplined the Scottish soldiers had become.
When King Robert returned his brother and his commanders criticized the king (as much as they dared) for risking his life that way. Robert the Bruce did not answer them. He only stared at his now broken battle-axe. Looking around the king saw English cavalry moving around their left. He pointed out the cavalry and said to Thomas Randolph "a rose has fallen from your chaplet". Immediately Randolph rode to his men and moved the schildton onto the open ground in the path of the English knights. When their leader Sir Henry Beaumont saw the Scots approaching he said "let us wait a little; let them come on; give them room." Sir Thomas Gray replied "I doubt that whatever you give them now, they will have all too soon." Sir Henry said to Thomas Gray, "if you are afraid then be off!" Sir Thomas replied "it is not from fear that I shall fly this day" and along with several other knights charged the Scottish schiltron. Many were killed, being impaled on the spears. Sir Thomas himself was captured. The remainder of the English knights surrounded the schiltron and attacked the Scots from every angle. But the schiltron held and the English in frustration began throwing their weapons at the Scots. When Sir James Douglas, commanding the left schiltron saw his friend in trouble and begged Bruce to go to his rescue. But by the time he returned to his man Randolph was winning the day. Moving forward Randolph's schiltron split the English cavalry in two. Half of the remaining English fled back to the English lines while half fled to Sterling Castle. After losing just one Yeoman, the Scots took off their helmets to rest from the heat of the day.
Sir Alexander de Seton had secretly left the King of England's Army and came to Robert the Bruce that night. He wished to no longer serve the king of England and offered to join the Bruce. He pledged on his life that the English were discouraged and if Bruce attacked them tomorrow, he would win the battle.
The English moved from the bogs south and east of the burn to harder ground. They had to water all the warhorses, draft horses and oxen. By the time the move was finished it was nearly dawn. But the tidal rivers around them had risen and they could not cross them as they did earlier. The English were now cramped into a small space where they could not move freely.
Robert the Bruce saw where the English spent the night. Their narrow front gave the Scottish army an advantage if the English did not move before morning. Morning found the English had not moved. Not long after daybreak on 24 June, three Scots divisions came out of the woods and began moving towards the English. The English mounted their horses in great confusion. When the Scots schiltrons began attacking the English lines the knights and soldiers could not maneuver. They were so crowded men were being pushed into the Bannock burn behind them.
Overnight the Earl of Gloucester and Edward II had been in an argument. Gloucester thought the English soldiers should rest another day before doing battle. The king accused him of being disloyal. Gloucester was still angry when the trumpets sounded the signal to assemble. So without putting on his surcoat he mounted his horse and charged into the schiltron commanded by Edward Bruce. The Scots did not recognize him without his surcoat and so did not spare him. The Earl and several of those with him were killed trying to break through the wall of spears.
The other two Scottish divisions moved up to join Edward Bruce. Randolph moved up on Bruce's left side. James Douglas came up next to Randolph. Together all three schiltrons filled the narrow . They pushed forward into the confused English. Wounded horses without their knights were running back into the English lines. Edward's army was now so crowded they could hardly move. The Scots were pushing into them from the front. The back ranks were being pushed into the water and marshes.