The structure is built in dressed stone cut like brick. This choice probably points to the influence of the architectural traditions of the Muslim East, where brick was the chief construction material. The mosque looks like a fortress pierced with eight doors and studded with towers and bastions.
The Great Mosque in Kairouan

Every city in Tunisia has a Great Mosque, but the Great Mosque in Kairouan is the most important of all. It is the oldest Muslim place of worship in Africa and is commonly regarded as the fourth holiest site in Islam (after Mecca, Medina, and Jerusalem).