One of the many castles held by the Levantine Assassins at the time of the Third Crusade, the Citadel of Alep functioned as the main base of operations for the Assassins in 1190. Although the Ayyubid Sultanate controlled Alep during this period, the Assassins and Saracens cooperated with one another in the city, and the Assassins retained primary control of its fortress under the leadership of Al Mualim.
Hunt for the Chalice
In 1190, the Crusaders were conducting a furious search for the Chalice, a mysterious artifact rumored to grant the power to unite the factions of the war. They hunted an Assassin who acquired vital information on the relic, pursuing him all the way to the outskirts of Alep, where they killed him after forcibly extracting the intel from him. Immediately afterwards, they assaulted a nearby village with the intention of massacring all of its inhabitants. In retaliation, the Assassins sent their forces from the citadel to rout the Crusaders, shortly after one of their agents Altaïr Ibn-La'Ahad killed the commanding Crusader.
In the aftermath, Altaïr was briefed by Al Mualim on his new mission: to recover the Chalice to prevent it from falling into the hands of the Crusaders or Saracens.
Betrayal of Harash
While Altaïr was away, the Keeper of the Assassins, Harash, had been bribed by the Templars to serve as their spy. In the process, he corrupted his henchmen and allowed his Templar contacts to enter and leave as they pleased, even receiving them in the castle's very courtyard.
By the end of his mission, Altaïr had been informed by the Chalice, actually a woman named Adha, of Harash's treachery. He returned to Alep in the middle of the night, being sure to do so covertly lest he was no longer welcome thanks to Harash's influence. This, he accomplished by destroying the aqueduct before the gates with explosives, allowing him to slip inside while the guards rushed to extinguish the fires. Once inside, he disguised himself as a Saracen to make his way to the main courtyard unmolested. It was there that he found Harash conferring with a Templar knight, confirming Adha's report about his betrayal. Without further ado, Altaïr moved to assassinate him, sparking a duel that ended in the traitor's death.
The next year, Al Mualim had relocated back to Masyaf as his main headquarters.
The gates to the fortress was connected to a guard outpost via an aqueduct.
The core of the citadel consisted of a vast, open courtyard with an arena in the center and platforms with training dummies to the side. Overlooking this courtyard was the main office of the Mentor, with a balcony that jutted outwards over the yard. The office lacked windows and was entirely exposed to the air outside, and its roof was held up by colonnades to either side of the balcony. The route from the office down to the yard consisted of a flight of stairs followed by a large, wooden ramp that branched in two.