Islands in the Neolithic
Tale of the limpet
Editor Simon Denison
Few aspects of ancient warfare are more conducive to archaeological research than siege mining and countermining. Ken Wiggins reports
When thinking of siege warfare we imagine many things - the thunderous discharge of formidable artillery weapons, scenes of battering rams pounding city gates, or fearless warriors scrambling up ladders thrown against mighty ramparts. Shakespeare dramatises the full-blooded intensity of the battle for Harfleur in Henry V: 'Once more unto the breach, dear friends, once more / Or close the wall up with our English dead'.
However, ancient authorities such as the Greek historian Herodotus, describing the Persian siege of Barca in 510 BC, and the Roman general Julius Caesar on his capture of Avaricum in 52 BC, tell of a different kind of siege warfare, a type that was invisible and silent but no less dramatic. Men who were expert in underground siege methods laboured to outwit each other in subterranean passages known as mines and countermines.
The purpose of digging tunnels ('galleries') by miners was to collapse the walls of the besieged fortress, by burning ('springing') the timber props at the end of the gallery once the foundations were reached. This caused the walls to sink and split, allowing an assault to be made on the breach by main force, hopefully bringing the siege to a speedy conclusion.
In response to this fearful threat, the defenders had no choice but to send down counterminers to detect and break into the enemy's mines, to see them off before any damage was done.
There were three ways a mine and countermine could become engaged. First, if the countermine was driven above an advancing mine, the counterminers could dig through to the mine below and pump in water to flood the enemy's work. Second, if the countermine was driven below the mine, the counterminers could spring the end of their gallery, thereby collapsing the mine above. And third, the two galleries could break through head to head, leaving it to the courage of the opponents in hand-to-hand combat to decide the outcome.
Siege warfare involving mining was introduced to Britain following the Norman Conquest at the siege of Exeter in 1067. The same stronghold was besieged in 1136, when miners again attempted to demolish the walls. Archaeological excavations carried out in the 1930s at Bungay Castle, Suffolk, exposed a mine gallery over 7m long, dated by the excavator to the siege by Henry II in 1174. One of the most significant examples occurred at the siege of Rochester Castle, Kent, in 1215, when miners successfully brought a tunnel below the corner of the keep, firing the props, we are told, with the fat of 40 bacon pigs, and bringing the masonry crashing down.
The advent of gunpowder made mining more effective than previously thought possible, and the explosive mine eventually replaced the burnt-prop techniques of earlier times. Underground tactics were adopted at the siege of St Andrews Castle, Fife, in 1547. A mine dug through the solid rock below the castle was intercepted by a countermine, bringing the mining to an end. These structures were discovered intact in the 19th century, and form an essential feature of a visit to the castle.
Sieges became a staple of the Civil Wars between 1642 and 1651. The use of miners to bring about dramatic results occurred during attacks on walled towns such as Gloucester (1643) and York (1644), and also at hotly disputed castles, notably Wardour, Wiltshire (1644) and Sherbourne, Dorset (1645).
Some archaeological evidence for underground siege methods during the civil war years has come to light, such as the discovery of countermine shafts at Pontefract Castle, West Yorkshire, dating from the siege of 1645. However, the best evidence recovered to date comes from King John's Castle, Limerick, in Ireland, adding much to our understanding of the siege.
Siege of Limerick
This magnificent fortress on the Shannon River, with powerful round corner towers, high curtain walls and a twin-towered gatehouse, was an example of medieval military architecture at its most powerful, but the strength of the castle was not put to the test until the 17th century.
In October 1641 Irish Catholics took the difficulties then being experienced by King Charles as an opportunity to assert their independence, and rose in rebellion. Protestant and English settlers living in Ireland had to find shelter until the disturbances were quelled. The authorities in Limerick, the third largest city in Ireland, quickly identified themselves with the rebel cause, compelling many of the distressed English citizens to flee to the safety of the king's castle, under the command of its constable, George Courtenay, who belonged to the wealthy Courtenay family of Powderham Castle, Devon.
In May 1642 the Irish army was admitted to the city, and quickly placed the castle under siege. The struggle for possession of the castle lasted five weeks, ending with its surrender to the besieging Irish forces. Capitulation by the garrison was inevitable once the northern corner of the castle's artillery bastion was destroyed, something the Irish achieved without the firing of a single cannon shot.
The name of George Courtenay and the events of the siege of 1642 were all but forgotten when archaeologists went to work at the castle in 1990 as part of a major restoration project. Among the first significant discoveries made on the eastern side of the castle was a long trench-like feature defined by two rows of well-preserved timber props, and an enigmatic tunnel below the foundations of the curtain wall, where a half-buried pistol was found.
We had stumbled on unexpected evidence for the underground siege of Limerick Castle, but was it possible to understand what was really going on? Fortunately, several detailed eye-witness accounts of the siege still survive. The manuscripts bring the reader back to the tense hours and days of the siege, and contain many references to the digging of mines and countermines, making it possible for the excavated structures to be understood as part of a larger picture.
When the Irish army occupied Limerick in the weeks after Easter 1642, they had the upper hand in terms of numbers, but they had no guns of sufficient size to batter the castle into submission. They had to consider other ways of winning possession of the fort. It would not be easy, for although the garrison had very limited amounts of powder and shot at its disposal, the defenders were determined and capable of making a bitter fight of it. One option was to blockade the castle and wait for the garrison to be starved into surrender. However, the Irish needed the castle's large cannon for use in reducing other strongholds in the region, and were anxious to do so with the minimum delay.
Vulnerable to attack
The solution was to instigate attack by mining. Several conditions were favourable to the use of underground tactics. The castle was vulnerable to mining because of the presence of dwellings facing its northern side (Thomond Street), and to the east (High Street). Furthermore, the enclosing wall of a churchyard was only a short distance from the southern side and bastion. These structures provided miners with shelter, allowing them to begin their works in safety, and greatly reducing the distance to be traversed below ground to reach the walls.
The essential ingredient for a mining strategy was the availability of a skilled workforce. The work involved not only the digging of shafts and galleries below ground, but also the making of timber props to shore the mines correctly to prevent premature collapse.
The expertise the Irish forces needed was available in abundance. With the spreading of rebellion at the end of 1641, workers at the royal silver mines in Co Tipperary north-east of Limerick had little option but to travel to the city for protection. One miner, William Timmes, has left a hair-raising account of how he came to Limerick in 1641, was captured by Irish rebels, but managed to escape to the castle where he went to work in the countermines.
Some of the miners, either by choice or through coercion, elected not to put their trust in the uncertain sanctuary of the castle, and threw in their lot with the Irish, putting their talents to work in bringing about the capture of the castle, whilst their erstwhile colleagues applied themselves to its defence. In this way the digging and carpentry expertise was divided more or less evenly on both sides.
The garrison was well aware of the threat which mining presented. Before the siege began, they dug a trench about the castle, a large section of which was excavated in 1990, which they hoped would frustrate the Irish efforts to drive mines below the castle.
The opening day of the siege was 18th May. The first week went by without any hint of the mining danger that was to come. However, on the night of the 25th the lookouts reported sounds of 'digging, hammering and sawing' coming from one of the High Street houses, east of the castle, a sure sign that mining preparations were now underway. The garrison's response was to sink two countermines next to the eastern curtain wall on 30th May, with the intention of intercepting the incoming mines.
For Countermine 1, the garrison's first mining team opened the entrance shaft about 8m inside the edge of the eastern curtain wall, and sunk it to over 3m below the level of the courtyard. The gallery was driven eastwards from the bottom of the shaft through soft clay, becoming steadily deeper as it progressed towards the foundations of the wall. The counterminers inserted timber frames at regular intervals along the length of the gallery, made from alder, birch and oak.
A timber frame consisted of a baseplate, two props on either side of the tunnel and a top-plate, secured by mortise and tenon joints. The baseplates were found to be about 1.5m long. The excavated props had all decayed to varying degrees, but in some cases survived to over 1.6m long, indicating that the countermine was designed for walking rather than crawling through, albeit with a slightly crouched posture.
The timber frame formed a kind of doorway through which the digging of the gallery continued, and a new frame was installed every 40 to 70cm along the lengthening gallery. During the excavation of Countermine 1, we uncovered the remains of nine in situ frames in a distance of just over 5m.
To screen the sides of the gallery the counterminers inserted pointed timber strips in the spaces between adjacent pairs of props. Once slotted into position the strips remained tightly in place without having to be nailed or tacked on. Most importantly, the roof of the gallery had to be secured against collapse, which would be fatal to the miners working inside. To do this long timbers of all types were wedged into place above adjacent pairs of top-plates, ensuring that the overhead gaps were completely covered. The weight of the overburden, pressing down on the top-plates was enough to hold the roofing timbers firmly in position without any nailing together.
At the far end of Countermine 1, distinctive planks of Scots pine were used for roofing the gallery, probably obtained by ripping up floor-boards in one of the chambers in the castle.
The timber frame method was a very strong yet simple means of constructing underground galleries, and the same techniques seem to have been applied in all the mines and countermines built during the course of the siege. The timbers were roughly dressed by axe work, leaving some bark on the surfaces in many cases.
Countermine 2 was located just under 3m south of Countermine 1. It was sunk to a greater depth below the courtyard, around 5m, and the gallery advanced horizontally to the east, rather than gradually sloping. The counterminers probably used a ladder to climb in and out of the gallery through an entrance shaft just over 1m wide, and spoil was likely to have been taken out in baskets pulled up by rope.
Work in both countermines came to an abrupt end on 7th June, following a stroke of good fortune for the defenders. Mine 1, emanating from a house on High Street, made contact with the trench dug around the castle, breaching the roof of the mine. The defenders poured water from the top of the bastion, which flooded the end of the gallery, and caused the work to be abandoned. As we excavated the flooded end of Mine 1 we discovered the final timber frame installed in the gallery, confirming that the miners gave up about 6m short of their intended target, the eastern curtain wall.
The setback of 7th June encouraged the Irish to concentrate on making a decisive breakthrough along the southern side of the castle. However, on 12th June, having met further stiff opposition, they returned to the eastern side and commenced a number of new works. Mine 2 was aimed at the eastern curtain wall a good distance to the north of the bastion. Mine 3 was a branch of the recently abandoned Mine 1 gallery, and took another route towards the eastern curtain wall, although when it hit the base of the wall, it branched again to form Mine 4. One further mine - we can call it Mine 5 even though, sadly, it was not discovered during the excavation - was driven towards the northern corner of the bastion.
By this point in the siege, the garrison's supplies had dwindled to such an extent that there was only enough timber left for one new countermine. On 13th June, Robert Pope, now directing the countermining effort, decided to try and intercept Mine 2, and commenced work in Countermine 3. The two galleries converged and met below the line of the eastern curtain wall on 20th June.
Pope and his men appear to have lit a fire at the head of the countermine, the smoke from which confused the enemy miners, and in the ensuing gun battle the Irish were beaten back, giving Pope possession of their tunnel. The discovery of a pistol in Mine 2 during the excavations is dramatic confirmation of the ferocity of the struggle below ground on this occasion.
Pope's next action was to take down all the timber from the two galleries in order to start another countermine. This explains why excavations in Mine 2 and Countermine 3 found no in situ timberwork. Without pausing for rest, Pope began the final countermine of the campaign (Countermine 4), opening the shaft inside the sallyport of the bastion - but by that stage it was too late for disaster to be averted.
The undiscovered mine, Mine 5, successfully brought down the northern corner of the bastion in the early hours of 21st June, covering the adjacent area with limestone rubble. Mine 4 was sprung below the southern end of the eastern curtain wall later the same day. Several of the timber props excavated in Mine 3 were heavily charred as a result of this activity. Robert Pope's heroic efforts in Countermine 4 came to an end, and George Courtenay offered to negotiate terms of surrender. On 23rd June the leaders of the Irish army were admitted to the castle, ending one of the most dramatic sieges ever to take place in Ireland.
Although the siege was well documented, our understanding of it has been transformed by the discovery of high quality archaeological remains. The startling preservation of much of the mining timberwork gives the siege great immediacy and intimacy, communicating in a powerful way the nature of unfolding events that were more than words on a page in a history book, but traumatic experiences that had a profound impact on the lives of real people.
End of mining
The story of underground siege warfare does not end in the 17th century, as British skill in this business made an impact on many wars in Europe. Mining played a prominent role in sieges conducted by the Duke of Marlborough, for example at Tournai in 1709. During the Peninsular War in 1812 a permanent company of sappers and miners was established in the British army for the first time, and miners brought the siege of San Sebastian to a successful conclusion in 1813.
The ultimate British military mining operation came to a spectacular climax on 7th June 1917 when nineteen mines dug below Messines Ridge on the Western Front were exploded simultaneously, resulting in colossal devastation and the surrender of 7,000 German troops.
Tunnel mines of this type fell out of use thereafter, but were revived for a time in the Far East during the Korean and Vietnam wars. On a hill at Dien Bien Phu known as Eliane 2, a marker stands at the entrance to a mine from the siege of 1954, the last tunnel mine ever exploded.
Ken Wiggins directed excavations at Limerick Castle, and is the author of 'Anatomy of a Siege: King John's Castle, Limerick, 1642' (Wordwell/Boydell 2000) and 'Siege Mines and Underground Warfare' (Shire 2003)
CBA web:Jan/Feb 2005