The action took place on the high ground to the east of Fyvie castle. Montrose decided not to use Fyvie Castle, which was poorly fortified, and instead occupied the higher ground to the east of the castle, which included ditches and dykes that could be used as entrenchments.
Argyll's men attacked the hill and took the lower dykes, but Montrose ordered Colonel O'Cahan to drive them out. O'Cahan pushed back superior numbers of foot and supporting cavalry, capturing some much needed bags of black powder. Lothian, one of the Covenanter commanders, then sent five troops of horse in, but they fell back under musket fire. Argyll then mounted a cavalry attack, but Montrose withdrew his men to ground where they could not be seen by the horsemen, intending to lure them into a trap. However, the Atholl men fired too early before the cavalry had been fully drawn into the trap; the cavalry retreated, pursued by the Royalists who killed Lord Keith and at least forty officers. A third charge took place involving both a regiment of infantry and some troops of horse, and the Royalists were forced to retire back to the main body of the army, whom Argyll did not dare engage because they were on the high ground. That evening, Argyll withdrew about two miles. Skirmishing continued for at least another two days before shortage of feed for his horses caused Argyll to pull back two miles to Crichie. Montrose took this opportunity to withdraw, first to Turriff and then west into Badenoch and, from there, into Atholl (Reid 2003).
The contemporary accounts differ on numbers.
Royalist: Wishart says that Montrose had 1,500 foot and not more than 50 horse (Wishart 1893). Spalding at one point in his account comments that it was admirable that Montrose was successful at Fyvie, given that he had so few men, which is an odd statement to make in the light of his reporting lower Covenanter numbers. However, in a note alongside this entry the different number is given, in rather obscure terms, of '1,800 foot and horss by baggage horse' (Spalding 1851). Ruthven says Montrose had 1,600-1,700 men, including one troop of fifty dragoons, under Gordon (Ruthven 1844). Reid believes Montrose had 1,500-1,600 foot. Cowan (1977) gives Montrose 1,000 foot and fifty horse (Reid 2003).
Covenanter: Wishart says that Argyll had 2,500 infantry and 1200 horse. Spalding puts Argyll's forces at 1600 foot and 14 troops of horse (800 horse?). Ruthven reports that intelligence from prisoners taken by the royalists before the march to Fyvie indicated that Argyll had 3,000 foot and 800 horse. Reid calculates that Argyll had 2,000 foot and 'a considerable body of cavalry'. Cowan states that Argyll had 2,500 infantry and 1,000 cavalry (Cowan 1977).
The action took place on the high ground to the east of Fyvie castle. There are some differences between the commentators on the phases of the action, and the time it lasted, although there is agreement that the command of the higher ground was critical to Montrose's success.
Wishart, a friend and supporter of Montrose, thought that it would have been madness for Montrose to have gone onto the lower ground with so small a force. He reported that Montrose considered that to have shut himself up in Fyvie Castle, which was poorly fortified, was dishonourable and would undo the reputation he had gained in his recent victories. He therefore occupied the higher ground overlooking the castle, which Wishart describes as:
'rugged, broken with ditches, and dikes raised by farmers to fence their fields, in appearance like a camp' (Wishart 1893).
Patrick Gordon of Ruthven, another royalist, states that Montrose chose Fyvie
'as also because the country there was well provided of victual for his armie; and if his army [Argyll's] should intend ane surpryce, or force him to feight, the ground was more advantageous for the defendant than the assailzeant, having the river of Ithen on his right hand, a woode on his left hand, and a deepe hollow bruike that ran befor him, which served as a ditch or trich to brake the furie of an united charge of horsemen' (Ruthven 1844).
Reid says that Ruthven's description implies that Montrose was facing southwards, but, as Argyll's cavalry was quartered around Rothienorman and Auchterless, west of Fyvie, this initial position was abandoned in favour of a westward facing one on the high ground overlooking the castle. He believes that Ruthven's 'hollow bruike' is a stream 300 m south of the castle, with an area of dead ground at the foot of the hill created by a low rise between the castle and the hillside. There was a series of turf walls on the rise and the adjacent hillside, which Reid interpreted as being agricultural in nature (Reid 2003).
Wishart, who was in prison at this stage and therefore relying on secondhand information, stated that Argyll's men attacked the hill and took the dykes, but Montrose ordered Colonel O'Cahan to drive them out, which he did successfully, pushing back superior numbers of foot and supporting cavalry. O'Cahan was also able to capture some bags of powder, which was providential as Montrose was short on this. Lothian, one of the Covenanter commanders, then sent five troops of horse in, but they fell back under musket fire. That evening, Argyll withdrew about two miles. He renewed the attack the next day, but without conviction, and the only action was light skirmishes of 'flying parties'. Meanwhile Montrose's men were melting down all the pewter they had for balls. Towards the end of the second day Argyll withdrew.
Spalding describes the action in very general terms:
'thair was hot skirmishing betwixt the trouperis persewing the wood, and Montrose manfully defending his few forces against such ane huge multitude of horses and men. He like a skilful capitane issuis out of the wood, and returnit back again, and did grate skaith that day'.
His account goes on to talk of further hot skirmishing on Tuesday and Wednesday, with little loss to Montrose, but daily slaughter to Argyll's troops, with many wounded being taken to Aberdeen (Spalding 1851). He has the action extending over at least three days.
Ruthven states that Montrose's horse were away seeking provisions, when Argyll came into sight 'who draws up his armie upon ane hill without distance of schot and sends first a regiment of foote to force them, or to draw them from their strenth' He goes on to say that this regiment occupied a 'fald' or enclosure , allowing them to fire on Montrose's men, but they were in turn attacked by Royalist troops under Donald Farquharsone of Monaltrie, who beat them back 'with great loss and discredit and to the no small encouragement of the Royalists'.
Argyll then mounted a cavalry attack, but Montrose withdrew his men to ground where they could not be seen by the horsemen with the intention of luring them into a trap,
'and ceartanely of those horsemen there had not a man escheaped, for they had been invironed before they had known where they ware, and the deep hollow ditch or bruike at their backs'.
However, the Atholl men fired too early before the cavalry had been fully drawn into the trap and they retreated, pursued by the royalists who killed Lord Keith and at least forty officers.
A third charge took place, involving both a regiment of infantry and some troops of horse, and the Royalists were forced to retire back to the main body of the army, whom Argyll did not dare engage because they were on the high ground. He then retired three miles and did not take up the attack again (Ruthven 1844). According to Ruthven all this took place on one day.
Reid says that the constrained and partially wooded terrain meant that the fighting did not develop into a general engagement. Strathbogie's men deserted Montrose at the start of the fighting, and Lothian's Irish troops took the enclosures at the bottom of the hill before being easily repulsed by a Royalist counter-attack, probably by Monaltrie's men. Argyll then sent forward five troops of cavalry. The Royalists abandoned the position without a fight, apparently seeking to lead the cavalry into a trap. However, Inchbrackie's men fired too early from the woods and the cavalry pulled back. Royalist infantry pursued them, but were, in turn, attacked by Keith's cavalry troop. Keith was killed, but his charge enabled the other four troops to escape although the Royalists retook the enclosures. Argyll attacked again with both infantry and cavalry in the afternoon, but to little effect, probably because he was reluctant to use his inexperienced and poorly armed levies and without them his infantry force was not strong enough to succeed. Skirmishing continued for another two days before shortage of feed for his horses caused Argyll to pull back two miles to Crichie. Montrose withdrew, first to Turriff and then west into Badenoch and from there into Atholl (Reid 2003).
In Williams' account, Montrose took advantage of the trees, dykes and broken ground and also started digging new trenches. Gordon and the horse, when they returned, were probably posted to the rear of the Royalist position where the bluff merged with the high ground behind it and was more accessible to troops who might cross lower down the valley where that ground was firmer and thereafter circle round to attack the ridge from this direction. It was also likely that a further body of Royalist troops held the causeway south of the castle entrance. Two hundred Gordons ran when Lothian attacked the dykes at the outset, and Montrose asked both Farquharson and O'Cahan to attack. The fact that the attack by 500 cavalry was pushed back by musket fire emphasised the difficulty caused to Argyll's troops by the boggy and broken terrain (Williams 2001).