Alep

Alep was a city where an Assassin fortress was located during the Third Crusade. It was the place where Harash, the Assassin Order's second-in-command betrayed the Assassins and was later killed by Altaïr Ibn-La'Ahad. Al Mualim resided in this fortress until it nearly came into disarray. In 1190, Altaïr visited Alep twice.

High Middle Ages
The first visit was during Altaïr's return from an assignment. He found the fortress and a small village nearby besieged by Templars under Basilisk's command. After repelling the attack, Altaïr met with Al Mualim, who gave him a new assignment concerning the Chalice.

During his second visit to the fortress, it had been already corrupted by the traitor Harash, who established his own guards around it. Templars had also made their way inside. Despite Altaïr managing to cleanse the fortress, Al Mualim and the Order had to switch their residence back to their headquarters in Masyaf. Later, after Altaïr's failure at Solomon's Temple, it was mentioned by an Assassin informant in Damascus, during the assassination attempt on Abu'l Nuqoud. The informant asks Altaïr about Adha and mentions their past adventures in Alep, probably mentioning the time when Alep was the Assassin's temporary headquarters.

Trivia

 * Alep (or Aleppo) was the largest city in Syria and the third-largest in the Ottoman Empire (Constantinople being the largest, and Cairo the second largest).