The Hasan Mosque was commissioned by Ya'qub al-Mansur (reg. 1184-1199) to serve as the principal congregational mosque of the Almohad empire. In that year, Ya'qub al-Mansur celebrated a major victory over the Christian forces in Spain, and to commemorate his conquest he founded the Almohad city of Rabat at the fortress that was used as the Moroccan base during the war. The mosque was to be one of the new city's monuments to his victory, and it would have been the second largest mosque in the Islamic world if fully constructed. The mosque was unfinished at the time of Ya'qub's death four years later in 1199, and his successors abandoned Rabat in favor of the more developed neighboring city Salé. The mosque was never completed and remains in a partially constructed state to this day.

The Hasan Mosque is notable for its immense scale; its footprint is larger than that of any medieval mosque excepting the Great Mosque of Samarra. Its plan is in the form of a large rectangle, 180 meters long north to south, and 140 meters wide east to west. The longitudinal axis of the plan is rotated twenty-five degrees counter-clockwise from the north-south meridian to accommodate qibla orientation, a degree of rotation similar to that of other mosques constructed under the Almohad empire. The mosque is located on a sloping site, and a huge raised platform was built out from the highest point on the slope to create a flat elevated surface upon which to construct the mosque. The large square minaret, 15 meters to a side, is located in the center of the north elevation, on axis with the mihrab. Four stairways are located on the north elevation, two flanking each side of the central minaret. These stairways lead from the surrounding neighborhood below to the edge of the mosque platform, where an arcade was planned to allow multiple points of entry to the mosque via a central sahn. Four additional stairs are located toward the north of the west elevation, and three others along the east elevation. At the south end of the complex, the mosque platform becomes level with the surrounding ground plane.

The interior of the mosque is structured as a vast hypostyle hall, with equally sized columns placed throughout the space on a grid plan. The central prayer hall is 21 arcade bays wide, each bay 6 meters wide east to west with columns spaced at 6 meter intervals. The central arcade and the outermost arcades that form the east and western edges of the mosque are slightly larger, each 10 meters wide. The mosque follows the T-shape plan that is typical of Maghribi mosques, with three 10 meter wide transverse aisles running parallel to the qibla wall. As the mosque was never completed, no more was ever built of the structure than the bases of the columns; today the mosque platform is defined by the unfinished grid structure, such that the plan is visible in the incomplete columns but no volume is enclosed. At the northern end of the mosque, there is a central sahn that is 11 arcade bays wide east to west and 7 arcade bays deep north to south, although no arcades were ever actually constructed to frame the east and west edges of the sahn. While this sahn is sizable at 70 meters wide and 42 meters deep, it is relatively small compared to the vast covered area of the mosque, again typical of Maghribi mosques. The unorthodox inclusion of two additional sahns closer to the qibla wall addresses the need for light and air in the enormous prayer hall that could not be met by the northern sahn alone. These courtyards were gender-segregated and provided distinct open air spaces within the mosque for men and women. The secondary sahns are each 6 arcades wide east to west and 11 arcades deep north to south, abutting the transverse arcades to the south and the outermost arcades to the east and west of the mosque.

As the mosque never progressed beyond the earliest stages of construction, no decoration was ever applied to the main structure. However, the incomplete minaret features delicate sculptural relief work on all four of its faces. The minaret as built is 44 meters tall, although it was likely intended to reach twice that height. The tower is typical of other Maghribi minarets in employing ramps instead of stairs for its interior circulation, as well as in its decorative use of latticework of carved blind arches. The surfaces of the square sandstone tower feature fields of finely-scaled interlacing polylobed arches, resolving at their lowest points into projected arches that frame recessed surfaces. Within these recesses, small slit windows topped by horseshoe arches allow a minimal amount of light into the interior spaces of the minaret. The exterior ornamentation of the Hasan minaret recalls that of the Giralda minaret in Seville, built twenty years earlier by al-Mansur during his occupation of the city in 1172.

Although it remains unfinished, the Hasan mosque is one of Rabat's most famous structures. The monumental scale of its plan was unmatched in the Maghrib at the time of its construction, and its minaret, though incomplete, is one of the most highly regarded examples of western Islamic minaret design.

Sources:

Bonine, Michael E. 1990. "Sacred Direction and City Structure." Muqarnas VII: 52.

Bosworth, Clifford Edmund. 1996. The New Islamic Dynasties. New York: Columbia University Press, 39-40.

Ettinghausen, Richard and Oleg Grabar. 1994. The Art and Architecture of Islam: 650-1250. New Haven: Yale University Press, 140-143.

Hillenbrand, Robert. 1999. Islamic Architecture. Edinburgh: Edinburgh University Press, 87-90, 140-142, 475.

Yeomans, Richard. The Story of Islamic Architecture. Reading: Garnet Publishing, 92-93.

"Almohad" The Grove Encyclopedia of Islamic Art and Architecture. Ed. Jonathan M. Bloom and Sheila S. Blair. © Oxford University Press 2009. The Grove Encyclopedia of Islamic Art and Architecture: (e-reference edition). Oxford University Press. Massachusetts Institute of Technology (MIT). http://www.oxford-islamicart.com/entry?entry=t276.e89.
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"Morocco, Kingdom of" The Grove Encyclopedia of Islamic Art and Architecture. Ed. Jonathan M. Bloom and Sheila S. Blair. © Oxford University Press 2009. The Grove Encyclopedia of Islamic Art and Architecture: (e-reference edition). Oxford University Press. Massachusetts Institute of Technology (MIT). http://www.oxford-islamicart.com/entry?entry=t276.e625. [Accessed October 31, 2009]

"Rabat" The Grove Encyclopedia of Islamic Art and Architecture. Ed. Jonathan M. Bloom and Sheila S. Blair. © Oxford University Press 2009. The Grove Encyclopedia of Islamic Art and Architecture: (e-reference edition). Oxford University Press. Massachusetts Institute of Technology (MIT). http://www.oxford-islamicart.com/entry?entry=t276.e771.
[Accessed October 30, 2009]