In the two years since the outbreak of the revolt in September 869, the Zanj had successfully spread throughout the districts of lower Iraq and al-Ahwaz, bringing much of the region under their control.

[2] After mid-870 the leader of the rebellion, 'Ali ibn Muhammad, was no longer personally leading the Zanj armies into battle; he instead resided in his newly built city, al-Mukhtara, and issued orders to his military commanders in the field.

These men were sometimes able to score a military victory against the rebels, but more often they suffered defeat, and in any case they were unable to effectively hinder the operations of the Zanj throughout the region.

In 871 Mansur ibn Ja'far al-Khayyat was appointed as the administrator of Basra and the Tigris districts, but he was similarly incapable of making any headway against the Zanj, and his troops suffered significant casualties at the hands of the rebels.

Although the Zanj had failed to take it at that time, a significant number of Basrans were subsequently killed at the Battle of the Barges, and the city was thereafter forced to rely on the Abbasid government to send troops for protection.

[12][13] In order to weaken Basra, the Zanj placed the city under virtual siege, harassing it with attacks day and night and destroying the surrounding villages.

The Basrans themselves had organized their own defense force headed by Burayh, a minor member of the Abbasid family and a resident of the city, but they were heavily suffering from hunger and disunity.

'Ali ibn Aban's troops were split into two contingents; one was placed under the command of Rafiq and ordered to attack the district of the Banu Sa'd, while the other was led by 'Ali himself and headed for the western suburb of al-Mirbad.

In the Banu Sa'd district, a small group of faction fighters attempted to mount a defense, but they were easily overwhelmed by cavalry and infantry attacks.

The government commander Bughraj's forces, supported by several Basrans, were split between al-Mirbad and al-Khurayba, but they were ineffective at halting the rebels' advance.

On Sunday morning Yahya ibn Muhammad attempted to launch a fresh assault against the city, but Bughraj and Burayh blocked his way and forced him to retreat, and he spent the rest of the day holding his ground.

Yahya ibn Muhammad also ordered one of his companions to collect a number of ovens, which the people assumed would be used to prepare food for them, as they were suffering from hunger.

After the massacre was complete, the Zanj spent the morning and afternoon searching for anyone else they could find; anyone who was rich was tortured in order to extract their possessions and then put to death, while the poor were killed immediately.

At the same time, the mosque and city port were burned down on the orders of 'Ali ibn Aban, resulting in further casualties and the destruction of goods, merchandise and livestock.

He appointed Yahya in command of Basra, but recalled 'Ali ibn Aban after the latter had shown some leniency toward some residents of the Banu Sa'd district.

The exact death toll is unknown; a figure of 300,000 given by al-Ma'sudi[38] has been rejected by modern historians as excessive, while other authors have cited numbers ranging between 10,000 and 20,000.

[3] The Zanj leader 'Ali ibn Muhammad celebrated the victory; he declared that his troops had been assisted by divine intervention, without which "the destruction would not have reached the vast proportions that people speak about.