The weapons and techniques used throughout most of siege warfare are remarkably consistent with few innovations. The notable new weapons were the trebuchet, Greek fire, and Cannons.
           Siege towers or belfries were common if unwieldy weapons used at sieges throughout the medieval period. They were often made of wood and were built taller than the walls they would be used to assault. Sometimes towers were wheeled or they could also be built on sleds so that they could be pushed up against the walls. The most difficult part of using a tower was getting it up to the walls in the first place as most towns and castles were protected by ditches or moats. These would have to filled in and leveled out before a tower could be moved into position.
Towers were used to shelter battering rams as well as to assault the walls over drawbridges from the upper stories. They were often protected by wet animal hides or sometimes even by tying hostages to the face of the tower. Defenders would attempt to destroy the towers by hurling stones at them, setting them afire, or even sometimes storming the tower in a sortie from the walls.
           There were many different shooting weapons used throughout the Middle Ages. It is difficult to determine the exact weapon medieval chroniclers speak of because of the way in which they would the use the same word to describe different engines. Generally historians have settled on there being three different mechanically powered weapon used in the Middle Ages the trebuchet, ballista, and mangonel.
           The ballista was known from ancient times and was a sort of outsized crossbow; in fact, some historians think that the crossbow is directly descended from the ballista. Most ballistae were constructed using two separate arms that employed skeins of rope or hair to provide torsion. There was a rail on which a bolt or stone was placed and the ballistae was fired with a trigger. It could be aimed precisely and its projectiles were fired with great force; there are reports of several men being impaled on one bolt from a ballista. The ballista was also used by the defenders of towns and castles as it could easily be mounted on walls due to its relatively small size.
           When the average person thinks of a catapult, what he is really thinking of is the mangonel. The mangonel was usually built an a platform either wheeled or on sleds, on which a long beam was fixed, with a cup at one end and the other end fixed into rope, hair, or gut for torsion. When fired the beam would strike a crossbar thus projecting the contents toward the target. Any number of things besides stones could be thrown with a mangonel and they often were. Projectiles used included but are not limited to dead animals and people, pots of burning pitch, the heads of enemy soldiers, and just about anything else disagreeable that medieval man could think of. The mangonel was used throughout the Middle Ages as well.
           A new throwing machine that appeared in the thirteenth century was the trebuchet. Trebuchet’s were the heavy artillery of there time, able to throw large stones a considerable distance with great force. They were built using a long beam on a pivot that was one third up the length of the beam. A counterweight was attached to the short arm and a sling was attached to the long arm. The weight of the counterweight pulled the long arm up and around causing the sling to release its projectile. Trebuchets could launch massive stones 200-300 yards with enough force to break walls and collapse towers. Beginning in the thirteenth century trebuchets began to be used all over, Europe and they were used until the end of the Middle Ages.
           Greek fire was a flame weapon used by the Byzantines starting about the eighth century it did not begin to be used in Europe until after the crusades. The exact formula is unknown but it is known that naphtha and quicklime were used. It burned even when doused with water and was either thrown in pots or projected in spouts. Greek fire was used: but never became a particularly popular weapon because of the difficulty of using it safely.
           The last siege weapon to make its appearance during the Middle Ages was the cannon. Starting in the fourteenth century and becoming more predominant as gunpowder technology improved. As the destructive power of cannon came to be appreciated, their use came to predominate in late medieval sieges such as Constantinople in 1453 and Malta in 1565. Cannon were not considered revolutionary at first because they were very dangerous to operate and as ponderous if not more so than their predecessor engines.
           Early cannon were constructed using iron rods placed around a central core and welded together. They were not very good and extremely dangerous to their operators because of the likelihood that they would burst when fired. As cannon developed they began to be cast in one piece of iron or bronzed which was safer although they were still liable to explode if fired to rapidly since they would then not be allowed the time to cool down properly. Their were some experiments with breech-loading cannon but these were found to be even more subject to bursting and eventually breechloaders were abandoned in favor of muzzle-loading cannon.
           What is amazing about medieval siege technology is not so much the progress but the similarity of medieval techniques with those of antiquity. A large part of the Middle Ages was spent relearning the techniques of the Romans although there was some innovation as the invention of the trebuchet, Greek fire, and cannons represent.