The siege of Azaz (15 May-21 June 1176) was one of a series of successes for Saladin in the aftermath of his victory at the battle of Tall as-Sultan (22 April 1176) and helped put pressure on the authorities in Aleppo (Saladin's Conquest of Syria).
After the death of Nur ad-Din in May 1174 his kingdom in Aleppo had split in three. His nephew Saif ad-Din, ruler of Mosul, renounced his allegiance to Nur ad-Din's heir as-Salah and invaded the lands ruled by Aleppo. The young king himself ended up at Aleppo, where Saif ad-Din's former general Gümüshtigin held power. The authorities at Damascus invited Saladin, then the ruler of Egypt, to take power in the city.
Saladin had to fight to establish himself in Syria. Aleppo and Mosul united against him in 1175, but their armies were defeated at the battle of the Horns of Hamah (13 April 1175). Aleppo acknowledged Saladin's position at Damascus, but Saif ad-Din hadn't been present and the battle and refused to accept the agreement. He convinced Aleppo to join him in a second attack on Saladin, but once again the combined armies were defeated, this time at Tall al-Sultan (22 April 1176). Saif ad-Din had been present at this battle, and was lucky to escape.
Four days after the battle Saladin appeared outside Aleppo, but this time he didn't plan to attack the city, having been repulsed during his siege of Aleppo of 30 December 1174-March 1175. Instead he appears to have decided to isolate the city. He moved north to attack Manbij, where the governor agreed to surrender the town as long as he could leave with his treasure. This still left a fortune in the town, and for once Saladin took a large share himself. Both Saladin and the governor's favourite son were called Yusuf. Some of the money was in bags with the boy's name written on it, and Saladin couldn't resist claiming this as money that had been put aside for him.
After taking Manbij Saladin moved west to Azaz (north-west of Aleppo, in the far north-western corner of modern Syria). This was a strong fortress, and its capture would both help isolate Aleppo and make it more difficult for the Crusaders to interfere (it had been a Crusader attack on Homs that had forced Saladin to lift his first siege of Aleppo).
The siege began on 15 May 1176. It lasted for thirty eight days, and saw Saladin use heavy siege equipment, including mangonels. The main reported incident of the siege was an attack on Saladin by assassins sent by Sinan, the 'Old Man of the Mountain' and head of the assassins. On 22 May Saladin was in his tent when one of the assassins managed to get close enough to strike him. Saladin was wearing his armour, so survived the blow. The first assassin was killed, but two more attacked. Both were eventually overpowered and killed, although one of Saladin's supports died as a result of his wounds. After this close-call Saladin had a wooden tower built (in some sources this was an enclosed bed, in others the tower was built around his entire tent). Later Saladin attempted to destroy the Assassins at their main stronghold. Although the attempt failed some sort of agreement must have been made, for the attacks stopped.
Azaz fell on 21 June 1176. Saladin appointed his nephew to command the fortress. He then turned back to deal with Aleppo. This move may have caught Gümüshtigin by surprise, for he was at Harim, west of Aleppo, either to guard against an attempt to further isolate Aleppo or possibly to avoid a direct clash with Saladin. Saladin's move to Aleppo might have been in response to Gümüshtigin's absence, or it might have been triggered by his anger at the Assassin attack, but in either case it was effective. The defenders of the city didn't want to risk a second siege, and quickly came to terms with Saladin. On 29 July the authorities in Aleppo officially recognised Saladin as king in Damascus.
After the peace had been agreed as-Salah sent his sister to plead for the return of Azaz. Saladin had already returned the lands around the fortress, and he now agreed to return the castle as well. This move helped improve Saladin's reputation in Aleppo.
After the twin triumphs at Tall as-Sultan and Aleppo Saladin was finally secure enough in Syria to return to Egypt. After a brief stop at Damascus he left for Cairo, where he made a triumphant entrance on 22 September 1176. His attention now turned towards the Crusader kingdoms, and in the following year launched a first attack on Jerusalem which ended in defeat at Ramlah or Montgisard.