Adrian J. Boas
On Defying Gravity
We should be very pleased that there is gravity holding us onto the world. Gravity is essential for the existence of life on the planet, and how wonderful that it does so in such a gentle fashion so that we don't feel a thing, and there is no sense that we are being pulled onto the surface of the earth by a sort of powerful magnetic force. If it were not for this remarkable phenomenon we would go flying off into the blue, which would certainly put a damper any plans we might have, and who knows where we might end up? One of the downsides of gravity (excuse the pun) is that it makes it difficult to lift heavy things. The heavier they are and the higher we wish to raise them, the harder it becomes to get them where we want. Fortunately, today technology enables us to overcome gravity and do such remarkable feats as to go hurtling up into the heights of a skyscraper in an elevator, lift a Jumbo jet weighing 447,700 kilograms into the sky, and send a 381-kilogram Mariner Mars Mission craft on its 3,431-kilometre voyage into space. With such achievements it is hardly surprising that we take a great deal for granted, and if observing a building project, we see a crane lifting heavy concrete beams to great heights, we hardly give it a second thought.
I have always had a special fascination with cranes. When I was about seven or eight, I was given a bright yellow toy crane with black pulleys and cords. It was, I think, my most treasured birthday gift. Many years later, visiting the city of Gdansk on the Baltic Sea I was fascinated by the iconic port crane, reconstructed after damage in the Second World War. Originally built in the fourteenth century, it was rebuilt in the fifteenth and in use until the nineteenth. Its interior contains two giant treadwheels (magna rota) on the ground floor and two more on the fifth floor, each of which is 6.5 metres in diameter. They could raise loads of four tons to eleven metres high and had maximus lifting height capability of 27 metres.
What brings this to mind is my recollection of the sense of awe when observing the enormous stones that formed the vaulting system at Montfort. The huge ashlars used in constructing the piers that supported the vaults weighed as much as two tons each, and just getting them to the castle from the quarry over a kilometre away via the narrow track down a fairly steep decline was a substantial achievement in itself. The individual segments of the ribs were hefty and, as can be seen in the above photograph, so too were the keystones that held the ribs in place. Getting these up and into their position during construction would have been a pretty impressive feat of engineering. The stone seen above was one of four huge keystones with decorated bosses that held up the four groin vaults of the ceremonial hall at the western end of the castle. Each of these had to be winched into place during construction about eight metres above the floor of the hall, and twice that height from the ground level. And there was another story above the hall with similar vaulting, though of slightly smaller stones. Most probably raising these pieces was done using a treadwheel, and the use of such mechanisms in construction in the Latin East is suggested by their appearance in an illustration in a late thirteenth century manuscript - the Histoire Universalle that was a product of the scriptorium at Acre. More substantial is the archaeological evidence for the use of such cranes that is found in two of the great Hospitaller fortresses. Two round stone crane bases were found at Margat in northern Syria and another even larger one at Crac des Chevaliers. On a more modest scale, there is also evidence to suggest the use of small cranes in castle construction. In the excavations we carried out at Templar Vadum Iacob in 1994, the mechanical removal of soil against the fortifications on the north side of the castle exposed a section that showed how that earth had been piled up in sloping layers against the external face of the wall as it was being constructed. Every two or three courses this pile of soil had been levelled off with lime to form a road on which large ashlars were brought and then raised into position, presumably by the use of small cranes, after which additional soil was dumped and the process repeated.