Coin Struck in Al-Khayzuran's Palace 908-810, Baghdad, Iraq
The head of the harem was the mother of the caliph who ruled over it as a sort of personal court. Through her direct relation to her son, she could exert considerable control over the empire and act as an essential political player.
Most were originally enslaved concubines brought from outside of the Muslim world. After having borne a son to the caliph, they could acquire the highly sought-after title of umm walad ("mother of the child/heir"). Though rare, in some cases she could even attain the status of a legal wife, even though the stigma of her enslavement remained and could always be invoked. For instance, al-Khayzuran, the wife of Caliph al-Mahdi and mother of Harun al-Rashid, was originally an enslaved Yemeni concubine. A coin bearing the name of her palace complex suggests that she acted as de facto ruler after the death of her husband.
Indeed, becoming the mother of the caliph would bring her considerable power and wealth. From the heart of the caliphal palace, umm walads used their network of servants, eunuchs, and entertainers to structure charitable foundations, fund important works of architecture and infrastructure, manage their own properties, and treat with potential political allies. But attaining this status implied political struggles.
After giving birth to her son, an umm walad's priority became convincing the caliph to name her child as official heir. This put her on a collision course with other women whose sons could claim the caliphal title, and their supporting factions. Unruly or rebellious brothers could be dealt with by assigning them to posts in distant territories. While fratricide was frowned upon as impious and therefore inappropriate for a ruler in the Abbasid age, conspiring to take the throne could in rare cases lead to execution.