The massive structure of the Great Mosque of Kairouan in Tunisia, also known as the Mosque of Uqba, illustrating the mixed influences of pre-Islamic, Roman and Byzantine architecture, is one of the oldest places of worship in the Islamic world. Standing with imperial grace in the centre of the country between the mountains and the sea, it is considered the fourth holiest site in Islam after Mecca, Medina and Jerusalem. The original mosque on the site was constructed by an Arab General and conqueror Uqba ibn Nafi or Sidi Okba as a Friday Mosque, after he founded the city of Kairouan in the area. However, shortly after its construction, around 690 AD, the mosque was destroyed during the occupation of Kairouan by the Berbers and was rebuilt in 703, by an Arab General Hassan ibn al-Nu'man of the Ghassanid or Jafnid tribe. However, after that, as Kairouan prospered with the increase of its population, the mosque was renovated, extended, even rebuilt at least twice during the eighth century. But the current structure of the mosque, resembling a fortress, can be traced back to the period of the Aghlabid dynasty, when in 836, Prince Ziyadat Allah I pulled down most of the earlier mud-brick structure and rebuilt it in more permanent stone, brick and wood. At the same time, the ribbed dome of the mihrab was also raised on its squinches, the triangular corners that support the base of a dome.

Covering a huge area of 115,660 square feet (10,800 sq m) the enclosure of the Great Mosque of Kairouan is interrupted by nine gates, six openings to the courtyard, two openings to the prayer hall and a ninth allows access to the maqsura or the wooden screen, located near the mihrab. With an interior dimension of 220 by 170 feet (67 by 52 m), the courtyard is a vast trapezoidal area, containing a horizontal sundial near its centre and is surrounded by a portico with double rows of arches, opened by slightly horseshoe arches, supported by reusing the columns from Roman, Early Christian or Byzantine monuments, particularly from Carthage. The northern part of the courtyard is paved with flagstones, while the rest of the floor is almost entirely composed of white marble slabs.

Standing on a square base of 35 feet (10.7 m) on each side, the 103 feet (31.5 m) tall minaret, reminiscent of the Roman lighthouses, is one of the city’s highest structures, which occupies the centre of the northern façade of the complex's enclosure and located inside the enclosure, without any direct access from the outside. Consisting of three tapering levels, its first and second storeys are surmounted by rounded ramparts, pierced by arrowslits, while the last storey is topped with a small ribbed dome, which seems to be built later than the rest of the tower. Obviously, apart from being used to announce the time for prayer, the minaret also served as a watchtower. The door of entrance to the interior of the minaret, framed by a lintel and jambs and made of recycled carved friezes of antique origin, leads to a staircase of 129 steps, surmounted by a barrel vault, leading to the terraces and the first tier of the minaret. The south façade of the tower, facing the courtyard, is equipped with windows to provide light and ventilation in the interior of the minaret and the other three are pierced with small openings in the form of arrowslits for defending the mosque against any possible attack. Considered the oldest minaret in the Muslim world Muslim, it is also the world's oldest minaret still standing.

Among the several domes of the Great Mosque of Kairouan, the largest is set over the mihrab and the entrance to the prayer hall from the courtyard. Reflecting Roman and Byzantine architectural styles of architecture, it is based on an octagonal drum with slightly concave sides, raised on a square base, decorated with five flat-bottomed niches on each of its south, east and west faces, with five flat-bottomed niches surmounted by five semi-circular arches. Constructed around 836 AD, the dome is one of the oldest and most remarkable domes in the western Islamic world.

Followed by a portico, adorned with a pair of arches, the rectangular prayer hall of the mosque, decorated with 414 columns of marble, granite or porphyry and accessed by 17 carved wooden doors, is located on the southern side of the courtyard. The central nave, resembling a triumphal alley and leading to the mihrab, is significantly higher and wider than the other sixteen aisles of the prayer hall and decorated by a double row of arches on both sides, supported on a pair of columns and topped by a decoration of floral and geometric patterns. Illuminated by magnificent chandeliers, the nave opens into the south portico of the courtyard by a monumental, but delicately carved wooden door, made in 1828. The walls of the mihrab, located in the middle of the southern wall of the prayer hall, are covered with 28 panels of white marble, carved and pierced with a diverse range of creepers and geometric designs, including ornamented representations of grape leaves, flowers and shells. However, though the excessively decorated mihrab is unique, its decorative panels are from the Syrian area, the lustre tiles from Iraq and the stylized floral patterns reflect the Byzantine and eastern Islamic examples.

Located in the UNESCO world heritage town of Kairouan in Tunisia, the Great Mosque of Kairouan with its hypostyle prayer hall now stands between the Rue de la Kasbah and the Rue el Farabi in the historic walled district of the Medina and looks beautiful at night, when the minaret is aglow with lights.