The Battle of the Blacks or Battle of the Slaves was a conflict in Cairo that occurred during the Rise of Saladin in Egypt, on 21–23 August 1169, between the black African units of the Fatimid army and other pro-Fatimid elements, and Sunni Syrian troops loyal to the Fatimid vizier, Saladin. Saladin's rise to the vizierate, and his sidelining of the Fatimid caliph, al-Adid, antagonized the traditional Fatimid elites, including the army regiments, as Saladin relied chiefly on the Kurdish and Turkish cavalry that had come with him from Syria. According to the medieval sources, which are biased towards Saladin, this conflict led to an attempt by the palace majordomo, Mu'tamin al-Khilafa, to enter into an agreement with the Crusaders and jointly attack Saladin's forces to get rid of him. Saladin learned of this conspiracy and had Mu'tamin executed on 20 August. Modern historians have questioned the veracity of this report, suspecting that it may have been invented to justify Saladin's subsequent move against the Fatimid troops.

This event provoked the uprising of the black African troops of the Fatimid army, numbering some 50,000 men, who were joined by Armenian soldiers and the populace of Cairo the next day. The clashes lasted for two days, as the Fatimid troops initially attacked the vizier's palace, but were driven back to the large square between the Fatimid Great Palaces. There the black African troops and their allies appeared to be gaining the upper hand until al-Adid came out publicly against them, and Saladin ordered the burning of their settlements, located south of Cairo outside the city wall, where the black Africans' families had been left behind. The black Africans then broke and retreated in disorder to the south, until they were encircled near the Bab Zuwayla gate, where they surrendered and were allowed to cross the Nile to Giza. Despite promises of safety, they were attacked and almost annihilated there by Saladin's brother Turan-Shah.

The defeat of the Fatimid troops was a watershed in the history of Egypt and the Muslim world, as it removed the main military support of the Fatimid regime and consolidated Saladin's position as the de facto ruler of Egypt. This culminated in the restoration of Sunni dominance over Egypt and the deposition of the Fatimid dynasty in September 1171. In its place, Saladin established his own Ayyubid dynasty. Some black African troops remained in Saladin's service for a few years but most who survived the massacre of 1169 fled to Upper Egypt, where they joined unsuccessful pro-Fatimid uprisings in subsequent years.

In the 1160s, the declining Fatimid Caliphate of Egypt was faced with invasions by the Crusader Kingdom of Jerusalem, domestic turmoil, and the intervention by the powerful Sunni Muslim ruler of Syria, Nur al-Din, who sent his general Shirkuh into Egypt. The complex political and military manoeuvring that followed ended in January 1169 with the appointment of Shirkuh as vizier by the Fatimid caliph, al-Adid. When Shirkuh died shortly after, on 23 March 1169, his nephew Saladin was chosen as a compromise candidate from the various factions of the Syrian army to take his place.

Saladin's position was far from secure. Shirkuh's Syrian troops numbered a few thousand and their upkeep was uncertain. Saladin could count only on the loyalty of the Kurdish commanders affiliated with Shirkuh, whereas his Turkish commanders, envious of his rapid rise, might defect. At the same time, Saladin found himself as head of government of a nominally Isma'ili state while himself being a Sunni leading a Sunni army, as well as a subordinate of Nur al-Din, whose championship of the Sunni cause against the Shi'ite Isma'ilis was well known. Saladin's intention to abolish the Fatimid regime was evident from the start, and the various factions and power groups within the Fatimid establishment, especially within the palace, were bound to oppose him. The Fatimid caliphs, although politically virtually powerless, were important symbolic figures, sources of legitimacy, and in command of enormous financial resources.

This obliged Saladin to tread carefully at first, making a serious effort to establish good relations with al-Adid and promote a public image of harmony between the two. This displeased Nur al-Din, who mistrusted Saladin's motives and refused to recognize his new position. Nevertheless, in order to safeguard the Syrian position in Egypt and guard against yet another Crusader invasion, on 3 July 1169 Nur al-Din sent new troops to Egypt, under the command of Saladin's older brother, Turan-Shah. They arrived in Cairo on 29 July.

In the meantime, Saladin gradually began distancing himself from the Fatimid regime, starting by introducing Nur al-Din's name in the Friday prayer after that of Caliph al-Adid. Al-Adid was relegated to a ceremonial role, and even publicly humiliated when Saladin entered the palace on horseback (hitherto a privilege of the caliphs). Saladin also began openly favouring his Syrian troops, awarding them military fiefs (iqta') for their upkeep, while withdrawing similar fiefs from the Fatimid commanders.

These moves aroused the opposition of the Fatimid elites, who rallied behind the black African eunuch majordomo of the caliphal palaces, Mu'tamin al-Khilafa. According to the medieval chroniclers, Mu'tamin made contact with the Crusaders, inviting them to invade Egypt. Saladin would be forced to confront them, leaving Cairo. This would allow Mu'tamin and his supporters to mount a coup to depose him, and then strike at Saladin's forces from the rear while he was facing the Crusaders. For this purpose, Mu'tamin reportedly used a Jewish messenger, who aroused suspicion in Saladin's men because his new slippers clashed with the rags he was wearing otherwise. He was arrested, and Mu'tamin's letters to the Crusaders discovered. Under torture, the messenger revealed his master's machinations.