Al-Zaytuna (literally, the Mosque of Olives) is…

Al-Zaytuna (literally, the Mosque of Olives) is the second mosque to be built in Ifriqiya and the Maghreb region after the Mosque of Uqba in Al-Kairouan.

The exact date of building varies according to source.

Ibn Khaldun and Al-Bakri wrote that it was built in 116 Hijri (731 C.E.)

by Obeid-Allah Ibn Al-Habhab.

A second source states that the Umayyad Hisham Ibn Abdel-Malek ordered the building; however, Ahmed In Abu Diyaf and Ibn Abi Dinar attributed the order to Hasan ibn al-Nu'man who led the conquest of Tunis and Carthage.

Most scholars agree that the third possibility is the strongest by evidence as it is unlikely that the city of Tunis remained a long time without a mosque, after its conquest in 698.

Thus the closest date is 84 Hijri (703 CE), and what Al-Habhab did was in fact enlarge the mosque and improve its architecture.