In March 1639, Lord General Alexander Leslie captured Edinburgh Castle for the Covenanters by having one of his entourage sneakily apply a petard to the castle gates under cover of his appeal to the governor for its surrender. According to the Scottish military historian David Caldwell, this “has to be one of the most remarkable and easy captures of a major fortress in the history of warfare“.

A petard was a bucket or bell-shaped device that was filled with explosives and held against a wall or gate before being exploded, it channelled the explosive force towards the target and as such was a very early form of “shaped charge” weapon. The word Pétard comes from the Middle French péter, to break wind, on the basis of the noise made by the weapon’s detonation. It has entered the popular lexicon from the works of Shakespeare, the phrase “Hoist with his own petard” coming from Hamlet, and means to fall into your own trap or foiled by your own plans, as the petard was often as deadly to those using it as to the intended target.

When war broke out in 1639 between King Charles I and the Covenanting Party in Scotland – The First War of the Bishops – the King had tried to hand the governorship of the castle to Patrick Ruthven, a prominent Royalist soldier. Like many senior Scottish soldiers he had learned his craft in the service of Gustav Adolphus of Sweden during the 30 years war. Ruthven was renowned for his drinking abilities – Gustav Adolphus had used him as a emissary on account of him being able to drink the opposition under the table and still retain his faculties – but sensibly refused the job on account of the poor defensive preparations of the castle. Ruthven also declined Charles’ offer of overall command of the Royalist forces in Scotland as he was not granted absolute authority over them. Instead the castle was held by its long term constable, Archibald Haldane.

Leading the Covenanting Army was Lord General Alexander Leslie, Earl of Leven, an immensely capable and respected general. Ironically he had formerly served under Ruthven in the Swedish Army and had risen to Field Marshall in that service, but now back home found himself on the opposing side.

Leslie arrived at Edinburgh castle with fellow former servants of the army of Sweden; the similarly capable Alexander “Dear Sandy” Hamilton – General of Artillery – and Robert Monro – General Major. They brought with them 1,000 locally-raised hagbutters (musketeers). Ostensibly they were there to either appeal to the garrison to surrender or to overawe them with their force. But they had a third plan in case either of these two failed; the petard.

Edinburgh Castle had been unsuccessfully attacked by the English under Hertford in 1544 when the towns of Edinburgh and Leith were burned. When Hertford, now the Duke of Somerset, returned in 1547 this time he didn’t even bother it. During the Siege of Leith, which lasted from 1548 – 1560, the Castle was held by the Queen Regent, Mary of Guise, and her Scottish Catholic and French supporters and was largely unaffected. War came again to the Castle in 1573 when a combined English and Scottish protestant force besieged it in the “Lang Siege” which brought the turbulence of the “Marian” civil wars to something of a close but also reduced much of the Castle and its defences to rubble.

Gordon of Rothiemay’s remarkable bird’s eye plan of 1647 shows the castle as it would have been in 1639, largely rebuilt since being reduced in 1573. It’s not so recognisable to us after all the Georgian and Victorian additions to the castle, but the obvious features of the royal apartments (a), St. Margaret’s Chapel (b) are there.

Defensively, the “Spur” (magenta) is the first line of defence. Built and financed by the French supporters of Mary of Guise in the 1550s and 1560s, it was a modern artillery fortification on the bastion style and protected the castle gates from direct frontal assault and had been rebuilt. The “Half Moon Battery” (green) was newer – built by Regent Morton after the Lang Siege – but with its rounded form was anachronistic.

The Spur had taken a siege lasting almost 2 years to overcome it; the Covenanters didn’t have anything like that sort of time or besieging resources on their hands, so subterfuge was a much more sensible approach. Leslie, Hamilton and Monro went up to the castle gates “between 4 and 5 in the afternoon” to parley with Haldane. As they withdrew, one of their party attached the petard to the outer gate of the spur and it was fired.

The outer gate demolished, the Covenanters’ forces rushed the spur in the smoke and confusion and quickly set about the 2 inner gates of the castle “with axes, hammers and ramming-leddirs” while others poured over the walls on scaling ladders.

The garrison were caught totally off guard and unprepared and seemingly no attempt at resistance was made. Within an hour, the castle was in Covenanter hands without loss on either side. We can only surmise how the Covenanters managed to fix and fire the petard without any of the defenders trying to stop them. Perhaps the defenders gave those renowned generals outside the gates too much deference and wouldn’t suspect that they might try any such trick. Given this amounted to the physical opening shot of The First Bishop’s War, everything up until this point being political manoeuvring, the defenders could be forgiven for not expecting an assault.

Or perhaps they didn’t even know what a petard was and what to look for. Apparently this was its first use in Scotland for a generation and only the third record of one being used at all. Petards had been banned – on pain of death – by King James VI after their use to blow up the gates of the Lord of Spynie’s house of Kinblethmont in November 1602.

Or perhaps they just didn’t underestimated their foes and didn’t respect the skill, determination and masterful planning that usually marked out Alexander Leslie.

Within a year and the conclusion of the First Bishop’s War (in the favour of the Covenanters), the Castle was back in the possession of the King and this time had to be put under proper siege by the Covenanters under Major Hugh Somerville (Leslie was in England with the main body of the Covenanter army) to take it. Defending it this time was Patrick Ruthven, who had made considerable preparations for such an event and was well supplied and garrisoned; there would be no quick trick to take the Castle this time. Ruthven held out for 3 months before a surrender was finally negotiated, both defenders and besiegers being bloodied by the experience. For his troubles, Ruthven was raised by King Charles to Earl of Forth.

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