The Great Mosque of Kairouan (in Tunisia), considered as the ancestor of all the mosques in the western Islamic world , is one of the best preserved and most significant examples of early great mosques. The Great Mosque of Kairouan is constituted of a massive square minaret, a large courtyard surrounded by porticos and a huge hypostyle prayer hall covered on its axis by two cupolas. The Great Mosque of Samarra in Iraq, completed in 847 AD, combined the hypostyle architecture of rows of columns supporting a flat base above which a huge spiraling minaret was constructed.