Siege tower A siege tower ( also breaching tower ; or in the Middle Ages a belfry ) is a specialized siege engine , constructed to protect assailants and ladders while approaching the defensive walls of a fortification . The tower was often rectangular with four wheels with its height roughly equal to that of the wall or sometimes higher to allow archer s to stand on top of the tower and shoot into the fortification . Because the towers were wooden and thus flammable , they had to have some non - flammable covering of iron or fresh animal skins . The siege tower was mainly made from wood but sometimes had metal parts . Used since the 11th century BC in the ancient Near East , the 4th century BC in Europe and also in antiquity in the Far East , siege towers were of unwieldy dimensions and , like trebuchet s , were therefore mostly constructed on site of the siege . Taking considerable time to construct , siege towers were mainly built if the defense of the opposing fortification could not be overcome by ladder assault ( " escalade " ) , by mining or by breaking walls or gates . The siege tower sometimes housed pikemen , swordsmen , or crossbow men who shot quarrel s at the defenders . Because of the size of the tower it would often be the first target of large stone catapults but it had its own projectiles with which to retaliate . Siege towers were used to get troops over an enemy curtain wall . When a siege tower was near a wall , it would drop a gangplank between it and the wall . Troops could then rush onto the walls and into the castle or city . Ancient use . The oldest known siege towers were used by the armies of the Neo - Assyrian Empire in the 9th century BC , under Ashurbanipal II ( r . 884 BC - 859 BC ) . Reliefs from his reign , and subsequent reigns , depict siege towers in use with a number of other siege works , including ramps and battering ram s . Centuries after they were employed in Assyria , the use of the siege tower spread throughout the Mediterranean . The biggest siege towers of antiquity , such as the " Helepolis " ( meaning " " The Taker of Cities " " ) of the siege of Rhodes in 305 BC , could be as high as 135 feet and as wide as 67 . 5 feet . Such large engines would require a rack and pinion to be moved effectively . It was manned by 200 soldiers and was divided into nine stories ; the different levels housed various types of catapult s and ballista e . Subsequent siege towers down through the centuries often had similar engines . But this huge tower was defeated by the defenders by flooding the ground in front of the wall , creating a moat that caused the tower to get bogged in the mud . The siege of Rhodes illustrates the important point that the larger siege towers needed level ground . Many castles and hill - top towns and forts were virtually invulnerable to siege tower attack simply due to topography . Smaller siege towers might be used on top of siege - mounds , made of earth , rubble and timber mounds in order to overtop a defensive wall . The remains of such a siege - ramp at Masada , for example , has survived almost 2 , 000 years and can still be seen today . On the other hand , almost all the largest cities were on large rivers , or the coast , and so did have part of their circuit wall vulnerable to these towers . Furthermore , the tower for such a target might be prefabricated elsewhere and brought dismantled to the target city by water . In some rare circumstances , such towers were mounted on ships to assault the coastal wall of a city : at the siege of Cyzicus during the Third Mithridatic War , for example , towers were used in conjunction with more conventional siege weapons . One of the oldest references to the mobile siege tower in Ancient China was ironically a written dialogue primarily discussing naval warfare . In the Chinese " Yuejueshu " ( Lost Records of the State of Yue ) written by the later Han Dynasty author Yuan Kang in the year 52 AD , Wu Zixu ( 526 BC - 484 BC ) purportedly discussed different ship types with King Helü of Wu ( r . 514 BC - 496 BC ) while explaining military preparedness . Before labeling the types of warships used , Zixu said : Medieval and later use . With collapse of the Roman Empire in the West into independent states , and the Eastern Roman Empire on the defensive , the use of siege towers reached its height during the medieval period . Siege towers were used when the Avars laid siege unsuccessfully to Constantinople in 626 , as the " Chronicon Paschale " recounts : At this siege the attackers also made use of " sows " - mobile armoured shelters which were used throughout the medieval period , and allowed workers to fill in moat s with protection from the defenders ( thus levelling the ground for the siege towers to be moved to the walls ) . However , the construction of a sloping talus at the base of a castle wall ( as was common in Crusader fortification ) could have reduced the effectiveness of this tactic to an extent . Siege towers also became more elaborate during the medieval period ; at the Siege of Kenilworth Castle in 1266 , for example , 200 archers and 11 catapults operated from a single tower . Even then , the siege lasted almost a year , making it the longest siege in English history . They were not invulnerable either , as during the Fall of Constantinople in 1453 , Ottoman siege towers were sprayed by the defenders with Greek fire . Siege towers became vulnerable and obsolete with the development of large cannon . They had only ever existed to get assaulting troops over high walls and large cannon also made high walls obsolete as fortification took a new direction . However , later constructions known as battery - towers took on a similar role in the gunpowder age ; like siege - towers , these were built out of wood on site for mounting siege artillery . One of these was built by the Russian military engineer Ivan Vyrodkov during the siege of Kazan in 1552 ( as part of the Russo - Kazan Wars ) , and could hold ten large - calibre cannon and 50 lighter cannons . Likely , it was a development of the gulyay - gorod ( that is a mobile fortification assembled on wagons or sleds from prefabricated wall - sized shields with holes for cannons ) . Later battery towers were often used by the Ukrainian Cossacks . Modern parallels . On 1 March 2007 , police officers were lifted to the upper levels of the building using small boom cranes in a manner similar to siege towers to enter Ungdomshuset in Copenhagen , Denmark . The officers were placed in containers which were lifted to the windows , thus enabling the police to gain access to the illegally occupied structure .