The fortifications of the citadel under the Zengids and Ayyubids
[Picture source: © Jean-Claude David ] [Picture source: © Jean-Claude David ] Under the rule of the Zengids, mainly Imad ad-Din Zangi (†1146) and his son Nur ad-Din Mahmud (†1174), the citadel must have seemed impregnable.
The captured Crusader, Renauld de Chattillon, was imprisoned in the citadel for 15 year before he was pardoned by As-Salih Ismail al-Malik (†1181), the son of Nur ad-Din. Baludin II, the king of Jerusalem, was imprisoned in the citadel for two years as well, as was Josselin II, Count of Edessa, who died here after nine years of imprisonment.
Which constructions were started under the dynasty of the Zengids is only partially known. They erected the “golden palace” on the citadel itself as well as a “green hippodrome” (green because the riding grounds were covered with grass). Nur ad-Din Mahmud, who was aware of the importance of strong city walls, renewed the walls of Damascus and Aleppo as well. Between two flanking walls at the entrance to the citadel, he built a steep riding staircase over which a horse-mounted rider could see.
Aleppo established itself as a trade center under the Zengids. When the Ayyubids succeeded them, the sultan Salah ad-Din (†1193) entrusted his son Malik as-Zahir Ghazi (†1216) to rule Aleppo. Az-Zahir Ghazi was a tested military commander and an astute builder of fortifications. In response to the persistent threats of the Crusaders, he fortified the citadel with then-state-of-the-art technology. The conflict with the Crusaders, which had lasted more than a century by that point, caused an arms race and thus new inventions in weaponry, such as the introduction of very strong trebuchets (counterweight catapults) (Fig. 2). In the 12th century they belonged to the arsenal of every successful siege. Launching projectiles of similar weight (50-300 kg) (Fig. 3) from the same location, they were able to pummel virtually the same spot, breaching even thick walls. The only preemptive measure was to strengthen the walls and to build ditches and barricades to keep attackers at such distance that their trebuchets could not be effective. The defenders started to use trebuchets themselves in the 13th century as well. This required the construction of large towers on the walls of castles and cities with platforms for trebuchets[1].
Figure 2: Trebuchets in action (around 1240) [Picture source: © New York, The Pierpont Morgan Library, Ms.683, fol. 23v (detail) from BRAUNE 2006, p.50] 
Figure 3: Aleppo, Citadel, inside: Ammunition for bliden stored in the upper gate area
[Picture source: © 2010 Michael Braune ] Due to their elevation, the walls of Aleppo’s citadel were not threatened by trebuchets but az-Zahir Ghazi still strengthened the walls, renovated towers and enlarged some in order to equip them with trebuchets. He also smoothed the sides of the hill, notably covering it with large stone panels around the entrance, the so-called stepped-stone-structure, which prevented the enemy from climbing to the towers. According to Ibn as-Shaddad, he opened a small entrance east of the gate, accessible from the palace, that he only used to reach the Dar al-Adl in the city for judicial purposes. This entrance was stumbled upon around 1990, during the restoration of the polygonal Mamluk tower though the Aga Khan Trust of Culture. In addition, az-Zahir Ghazi erected a rectangular (11 m x 17 m) tower (northern tower) (Fig. 4) close to the foot of the hill that was probably built on the foundations of the northern corner of the Ayyubid city walls. The defensive edifice is notable for rather thick wall on its exposed sides, designed to withstand trebuchet attacks, and a quite thin wall on the uphill side. The three-storey tower housed trebuchets that were covered by a stable barrel vault. The uppermost level ended in a flat and even platform, upon which were placed trebuchets and heavy ammunition. All storeys were equipped with deep niches through which archers could shoot arrows: the long sides that faced towards the battlefield had three niches, the narrow sides only two. The northern tower is a typical example of Ayyubid fortifications and similar design can be found on several Syrian castles.
Figure 4: Aleppo, citadel, outside: north tower, top view [Picture source: © 2010 Michael Braune ] A more difficult problem for az-Zahir Ghazi to overcome was the citadel’s water supply. In Aleppo the yearly precipitation is (based on 1914-2018 records) only 420 mm. Collected in the cistern, this amount was never enough to meet the yearly needs of the population for drinking water (min. 2 liter per day per person). The city had likely gotten its water from the Hailan-Aleppo qanat, a subterranean canal dug in pre-Islamic times. The source offered good drinking water but seldom enough of it for Aleppo’s population, especially in the summer months. The Mamluks later added water from the river Quwaiq was to the city’s resources. The citadel therefore was meagerly supplied from the rainwater collected in cisterns from roofs until the construction works of az-Zahir Ghazi (Fig. 17). Az-Zahir Ghazi now used the roofs of the newly constructed warehouses and granaries of his palace for the collection of rainwater that also forced him to construct a massive cistern. He also commissioned a well to be dug. A winding staircase (Fig. 6) around a square-shaped center led 225 steps or 50 meters underground. The depth of the well is unknown but it was partially refilled (Fig. 7) and probably fed from the Hailan canal via an inlet. A horse-powered lifting system could bring water from the deep well to the surface in the 18th century[2]. The water lifting system worked according to the principle of perpetual bucket chain (saqiya), the only possibility to mechanically transport water from great depths. This proven technique could also be observed in several Umayyad desert residences[3]. It is possible that there was a windmill on the citadel close to the deep well, which was mainly used to lift water to the surface, sometimes to grind cereals.
In another hydro-engineering measure, az-Zahir Ghazi had the ditch at the bottom of the hill deepened so that it could be filled from the north by the river Quwaiq. The excavation made it necessary to move the entrance of the citadel to another location. Az-Zahir Ghazi erected a rectangular lower gate tower, from which a slightly ascending bridge with eight arches connected it to the upper gate tower, which also formed the entrance to the citadel. If the intruder was able to cross the bridge despite the firing of six machicolations (a form of bretèche perfected by the Ayyubids), he stood in front of a two-winged cast-iron gate (Fig. 8). When the gate opened, one had to cross a dimly lit ca. 70-meter-long tunnel that changed directions five times, which was protected by arrow slits and dark niches, then two more iron gates before reaching daylight after again crossing a 23-meter-long hall (Fig. 9). Although gate entrances with changing directions belong to the standard inventory of the Orient since the Middle Bronze Ages (2180-1550 BC)[4], an entrance so well fortified by arrow slits from the top surely formed a masterpiece of Ayyubid fortifications.
The main road led from the upper gate tower to the small mosque and beyond that to the large mosque. Az-Zahir Ghazi build barrel vaults over the road so that the inhabitants could remain in the cool air of the shade, as in famous bazaar in the lower city. In tales, medieval castles are supplied by secret underground tunnels and emergency exits. The citadel of Aleppo actually had three underground corridors. They can be entered from the winding staircase of the well and led to the north. One ends underneath the previously described northern tower at the foot of the hill. The two other corridors led outside the citadel[5] but remained within the Ayyubid city walls. These are currently collapsed (2010).
The typical Ayyubid bivalve (double-layered) walls, with smoothed out ashlar blocks with carefully mixed filling material from mortar and rubble, could not withstand the strong earthquakes that struck Syria in the Middle Ages without damage. This is evident from the deep cracks and shifts in the walls. In 1225, ten towers (from the more than 40 standing today) collapsed east of the entrance (Fig. 10). These were probably some of the relatively small rectangular towers (5-6 meters wide, projecting 2 meters) that likely date from the Byzantine (9th century) or Hamdanid (10th century) period. Unstable ground was probably responsible for the collapse. This makes the re-erection of the towers on wooden foundations even more surprising, likely due to the fact that the defensive line on the edge of the hill could not be abandoned. The defenders paid dearly for this mistake in 1260, when the Mongolian commander Hulagu burned the wooden foundations, which collapsed the towers and allowed him to enter the defensive line on their former location. The so-called Mongol invasion of Europe brought an end to the Ayyubid dynasty. The Mamluk commander Baibars was able to defeat the Mongols and drive them out of Syria through lucky circumstance
