Bannockburn: the English Army
Note: There are some details about the Battle of Bannockburn that we may never know for sure, such as the numbers involved on either side, the actual battle site (although we are a lot nearer to a conclusion now thanks to the most recent dig), and how the terrain looked in 1314. This is because records have been lost (or never existed), and the contemporary accounts that do exist vary in their details. However, from all I have read I have put together the most likely scenarios.
By the autumn of 1313, Edward and his rebellious barons and earls had entered into an uneasy truce, which found Edward even forgiving those who had had Gaveston murdered (probably with his fingers crossed behind his back!). Some had been easier to persuade back into the fold: Pembroke and Gloucester had been disgusted by the actions of Lancaster and Warwick, and Hereford, too, seems to have had enough of opposing the king. Lancaster and Warwick, despite their pardons, still seemed to hold a grudge, a fact which became obvious very shortly.
With his nobility seemingly under control again, Edward had the chance to look towards Scotland and the plight of those suffering Bruce's oppression through raiding and protection money. The people of the north had sent him a letter begging for help and now it seemed that Edward was determined to do something about it, as well as relieve Stirling castle.
As early as November 1313, the king sent out writs to his earls and barons, ordering that they attend a muster at Berwick on Tweed by 10th June 1314. On March 9th demands were sent to the counties of the Midlands and the north for 4500 men, but this was superseded by another writ on March 24th for a levy of 16,000 foot from 13 counties. Throughout the rest of March more orders were issued: north and south Wales were to provide 5000 archers and spearmen, and Edward also sought help from the Irish. A summons was sent to the earl of Ulster and other Anglo-Irish and Irish lords. It is known that Ulster answered the call, and would have brought men with him, but it is less clear how many other Irishmen were at the battle.
If, in a perfect world, the levies had been filled and there were no deserters, then Edward could have expected to have had around 21,600 infantry and archers mustering at Berwick. However, it is certain that nowhere near that number actually got there. Sheriffs, overseeing the levy, were often unable to find enough men fit enough and of the right age. There was also a high rate of desertion at all stages.
Historians' estimates of the final number at Bannockburn range from about 5000 - which I think is far too low - to 16,000. This latter figure, based on previous summons and numbers of troops at muster is the most likely to be close to the actual number. It is also difficult, in the absence of specific records, to estimate the ratio of archers (both longbow and crossbow) to spearmen, as they are often both termed as 'infantry'. It is thought though, that Edward certainly had a large contingent of archers, the only effective weapon against Scottish schiltroms, as show in the battle of Falkirk in 1298.
The Cavalry
As with the infantry, it is impossible to know an exact number of mounted troops who fought for Edward at Bannockburn. In 1314, the cavalry charge was still the main method used for attacking an enemy - and usually the most effective. Edward had one of the best trained and equipped cavalries in Europe, something that should have been an asset to him against Bruce. For other battles, a fairly accurate estimate of mounted knights can be made through marshals' rolls, scutage and lists of warhorses taken to the campaign (as well as accounts of recompense for any horses lost afterwards). But for Bannockburn, we have none of these, mainly because there was no formal consent by parliament for raising the feudal host.
However, a start can be made by looking at the names of earls and barons that were there and coming up with at least a minimum number of the mounted troops they brought with them under their feudal duty to military service. From the accounts of contemporary chroniclers we know that five of Edward's earls, despite the peacemaking that had previously taken place, refused to attend in person. Instead Lancaster, Warwick, Arundel, Surrey and Oxford sent only the minimum troops required under the terms of their feudal duty. This means that these men, some of the mightiest in the realm, with some of the largest retinues, sent only about 60 knights to aid their king. Another small number of knights were also sent by prelates owing feudal service. This made a total of 150 from those two sources.
Luckily, Edward still had other earls and barons who stayed loyal and were present at Bannockburn, and they brought larger contingents of mounted troops with them. One record in the Rotuli Scotiae (Rolls of Scotland) does help us know the names of some of the knights present as contained in it are letters of protection for the earls of Gloucester and Hereford and other nobility, as well as nearly 900 men riding with them (their knights, esquires and lightly armoured horse-soldiers). However, this is not all of Edward's cavalry. Historian John Edward Morris has speculated that in addition to these names there would probably have been at least another 1000 -1500 mounted troops, making Edward II's cavalry around 2000-2500 in strength - a formidable killing machine when let loose on a battlefield.
Foreign Mercenaries
In most battles you find foreign mercenaries, and Bannockburn was no exception. In his epic poem The Brus, John Barbour mentions that the English numbers were swelled by knights from France, Gascony, Flanders, Germany and Brittany as well as Aquitaine and Bayonne. Again, we have no record of the actual numbers, but they are probably of no great significance.