Castle (12 page)

But if John was kept on his guard by his opponents, he was not content merely to cower behind his own defences. On the contrary, the king had also come equipped with the latest in siege technology, and his new toys were far bigger. Another very reliable and well-informed chronicler, the anonymous Barnwell Annalist, tells us that the king came to Rochester with ‘five throwing machines’. Without doubt, these machines were the heaviest artillery of the age: trebuchets.

Trebuchets were giant slingshots or catapults, deliberately designed and built to smash down castle walls. The idea of creating such a weapon was not new; machines that hurled missiles at masonry had been around for hundreds of years. Trebuchets, however, were a new twist on this old idea, a product of a revolutionary piece of thinking in the late twelfth century.

A man readies a mangonel
.

Throwing machines worked on one of two basic principles. Either they were powered by torsion, or they worked like a see-saw. Torsion machines had been in use since Roman times; the mangonel, for example, was a simple sprung throwing arm attached to a heavy wooden base, winched back, loaded and released. Similarly, the ballista
or
springald, a kind of giant crossbow, was another weapon used by the Romans that was still being deployed by both defenders and attackers in the Middle Ages. By contrast, machines which used the see-saw principle were a more recent development, but nevertheless were still well established by King John’s day. In the tenth century, the Chinese invented a simple device that became known in the West as a perrier. A triangular frame supported a long throwing arm, rather like a see-saw, but with the pivot very close to one end of the beam. To operate it, men would heave on a set of ropes that hung from the short end of the arm, sending the long end up into the air, hurling its missile skywards.

The trebuchet was a more sophisticated version of the perrier, devised by the Arabs in the course of the twelfth century. Rather than having its throwing arm flipped by men pulling on ropes, it relied on a large counterweight to perform the same function.

There are no surviving originals from the Middle Ages, but we do have pictures and diagrams of trebuchets in medieval manuscripts. Using this information, a team of historians end engineers has built
a
replica at Caerphilly Castle in Wales. Like a crossbow, the trebuchet is a machine which works on the principle of stored energy. The first part of the process involves heaving the counterweight – a wooden box filled with around two tons of earth and rocks – up and into place. A team of four or five men pulling on ropes can do this in about five minutes. Once the weight is raised and secured in place, the machine can be loaded. The missile – here a ball of cast concrete, but originally made of stone or lead – is then placed in the end of a sling attached to the long end of the throwing arm. When all is ready, a sharp pull on the trigger causes the counterweight to drop, pulling the short end of the arm downwards with tremendous force, hurling the long end upwards, and pulling the rope-sling after it.

A perrier
.

The whole motion, difficult to describe, is extremely elegant to watch; it looks like a cricket ball being bowled overarm. The surprising thing is the noise – or rather, the lack of it. Instead of the explosive charge of a cannon, and the whistling of the missile, there is just a scrape as the ball moves from under the frame, a shudder as the arm is stopped in its spin, and then – nothing. The ball moves through
the
air in total silence. It’s like watching a film with the sound turned off. The effect is utterly captivating: the motion of the machine and the arc that the missile describes are both exceedingly graceful.

The replica trebuchet at Caerphilly. The counterweight (within the frame) is raised by pulling the arm at one end and winching at the other
.

The Caerphilly trebuchet, it must be said, is an impressive beast. With a twenty foot-long throwing arm, it is a ‘full-sized’ replica, and its twenty-five-pound missiles would cause serious damage if directed against buildings (at Caerphilly, they splash down into the moat). It would have been quite possible, however, for medieval engineers to build much larger trebuchets – monster machines more than twice the size, with throwing arms up to fifty feet long. Very little could stand in the way of such huge weapons. Wooden buildings in a castle’s bailey would be smashed to smithereens. Lead roofs would offer no resistance. The only thing that might withstand a direct hit was masonry. Whether or not it did so would depend on a number of
factors
– how close the attacker dared to bring his engines, how large the machines were, and how heavy the missiles. It would also depend on the skill of the engineer and the precision of his catapult, since to bring down solid stonework would in most cases require several hits in the same place. Above all, it would depend on one question: how thick and well built were the walls?

The men inside Rochester Castle were now asking themselves much the same thing: would the walls of the tower, twelve feet thick, hold out against King John’s trebuchets? The Barnwell Annalist says that the bombardment of the keep did not cease by day or night. There is no suggestion, either from Barnwell or from any of the chroniclers, that the defenders were subjected to the kind of psychological and biological horrors we often hear about in other sieges. Sometimes rotting animal carcasses or the heads of fallen comrades were hurled over the walls of a besieged city or castle, in an attempt to spread plague and terror. John may not have resorted to such tactics (though one would hardly put it past him), but he knew, in any case, that the relentless barrage was piling psychological pressure on his enemies. As the stones rained down on them, as their food ran short, and as the winter cold began to set in, surely they could not hold out much longer?

And yet they did. Part of the reason for the rebels’ dogged determination was an earnest belief that the cavalry would arrive – either in the shape of Prince Louis, or in the more likely form of their London associates. According to one chronicler, the knights who remained in the capital had sworn to Albini and his colleagues that, should Rochester be besieged, they would ride to their aid. Up to a point, they kept their promise. Two weeks into the siege, a force of seven hundred horsemen left London and headed towards Rochester. Halfway there, however, their nerve failed; at Dartford, they turned and headed back. Why they did this is unclear, but it is possible that their scouts had returned with news of the size of the John’s army.
We
don’t know how large the king’s force was, but we can get some idea from the fact that seven hundred fully armed knights turned in fear and fled.

John would have learned soon enough that his other enemies had retreated back into their hole, and the news must have gladdened him somewhat. It was only a small consolation, however, because the fact remained that Rochester Castle and its defenders were still holding out, despite everything his expensive siege engines could throw at them. With every day that passed, it was becoming increasingly, maddeningly clear that the trebuchets were not going to work. The king, therefore, placed all his faith in his last remaining option: to drive a mine under the great tower, in the hope of bringing it crashing to the ground.

The technique of undermining was not a new one; the Romans and the Vikings are known to have used mines when laying siege to cities. The aim was to drive one or more tunnels under the foundations of the walls, supporting the ground above with timber props, which were then burnt away to create a collapse. But this wasn’t always possible. If the defences were built on solid rock, tunnelling underneath them was virtually impossible. Water defences, or even just soft or waterlogged ground, also meant that mining was out of the question. And even if the conditions for mining were ideal, conditions for miners themselves were anything but. The environment in which such men worked was dark, damp and dangerous: the process could easily end in disaster if the soil above them suddenly subsided.

Digging a mine in peaceful circumstances was difficult enough, but doing so during a siege was doubly dangerous, since the besieged would do everything in their power to frustrate the miners’ progress. Just getting close enough to begin digging would involve dodging a shower of arrows and crossbow bolts, so miners took care to approach under the cover of a ‘tortoise’ or ‘cat’ – a wooden canopy, moved on wheels, and covered in damp animal hides to prevent it
being
set on fire. Even once they were underground, the miners were still in danger of attack. Roman writers speak of defenders flooding enemy mines and drowning their assailants. A more common approach was for the defenders to dig a counter-mine, either in the hope of causing a collapse, or simply with the intention of meeting their opponents head on, and engaging them in subterranean hand-to-hand combat.

Luckily for John, his engineers reported that the ground around Rochester was suitable for mining. Even so, it was far from being an easy task. Despite having at their disposal all the picks that the men of Canterbury could manufacture, the operation was set to take weeks. At one point, progress ground to a halt when the miners came up against solid stone foundations – not those of the keep or the bailey walls, but the old Roman walls of Rochester. Only by making a detour could they continue with their tunnelling.

For the defenders trapped inside the keep, it was an agonizing waiting game. There is no indication that they tried any of the advanced techniques of counter-attack above, beyond of course trying to pick off miners with crossbows when they emerged from tunnelling. As with the trebuchets, they could only pin their hopes on the solidity of the tower and its foundations. These, we know, were profound; excavations in the late nineteenth century failed to find the bottom of the walls. Getting right underneath the keep must have been a hellish task.

Finally, however, John’s miners managed it. By 25 November, the mine was ready. Hundreds of tons of masonry were now supported only by wooden pit props. On the same day, John sent a letter to his trusted servant, Sir Hubert de Burgh. ‘We order you,’ he said, ‘to send us forty bacon pigs.’ This was not, however, the makings of a thank-you dinner for the hardworking miners – even a glutton like John would have struggled to finish that many ham sandwiches. The kind of pigs the king wanted, he went on to specify, were ‘the fattest
and
least good for eating’. It was not food that John was after, but fuel. The unfortunate animals were needed ‘to set fire to the stuff which we have put under the tower at Rochester’.

Once the mine was finished, it would have been stuffed with brushwood, straw and kindling to feed a great fire. How the pig fat was introduced is a matter of debate. An older generation of more imaginative historians envisaged the forty-strong herd being driven into the tunnels while still alive, burning torches tied to their tails. Sadly, modern military experts now think this unlikely; the idea of live pigs running around with firebrands attached is just too farcical, even for King John. It is now believed that the pigs were slaughtered and rendered down for their fat, which was subsequently poured into barrels and rolled into the mine.