The Great Mosque, once an important site of pilgrimage for Muslims, is the model for all mosques in North Africa and is thought to have the earliest and most beautiful prayer niche in Islam as well as a very early towering, square minaret. Its main structure and features remain in place from the 9th century and it is considered to be the most important monument of the Aghlabids left standing today.

Its sanctuary, or prayer hall, is made up of 17 arcades of 414 pillars in marble and porphyry, which were taken from various ancient buildings and as a result are all of different heights. They are connected by pointed horseshoe shaped arches.

Restoration took place n 862 when the mihrab, the prayer niche indicating the direction of Mecca, was added and decorated using rare, luster tiles imported from Baghdad. The pulpit is thought to be the oldest preserved example today. In the 13th century, the Hafsids added arcades around the courtyard and porches at the gates.