Mosque of Sidi Bel Hasan (Sayyidī Abū al-Hasan)

This mosque converted into a museum stands on the west side of the square adjacent to the Great Mosque of Tlemcen. This interesting model of Muslim art was erected in honour of Emir Abū Ibrāhīm ibn Yahyā Yaghmurāsan in 1296, after his death, as testified by the inscription engraved on an onyx plaque embedded in the western wall of the prayer hall in the middle of the third bay, and on plaques placed on two plaster panels forming the cyma moulding of the mihrāb. It is presumed that the current name of the building comes from the famous jurisconsult Abū al-Hasan ibn Yakhlaf al-Tanasī, a scholar who taught under the reign of Abū Sa‘īd ‘Uthmān (1283–1303).

This Abd al-Wadid mosque has modest dimensions, which may be explained by the presence of great sanctuaries in the city. Its plan is distinguished by the absence of a courtyard and bays lying perpendicular to the qibla. The prayer hall is divided into three naves and three bays determined by two rows of pointed arches resting on onyx columns, some of which are surmounted by magnificent capitals. The ceilings are made of cedar joists which simulate knotwork. They provide the first Algerian example of caissons, which were developed for three or four centuries in Muslim Spain.  .

The mihrāb opens in a horseshoe arch encircled by a rectangular frame surmounted by three openings that are fitted with openwork with finely wrought rosettes. Its arch moulding is a masterpiece of sculpture on plaster, filled with alternating floral and epigraphical motifs; from its spandrels spring out two delicate spiral cabochons on a ground of an eight-pointed star motif and running scrolls. This mihrāb marks the height of Hispano-Moresque art. It has a hexagonal plan and a cupola covered with muqarnas, a feature already used in the mosques of Qarawiyyin in Fez, Tinmal and Kutubiyya in Marrakech. Its niche, which starts from an octagonal plan and culminates in a small fluted cupola, is made up of curved openwork rectangles, lozenges, triangles, and pear-shaped motifs.

The lower part of the capitals is decorated with a hooked meander, a stylisation of the ancient acanthus wreath, while the upper part, which is parallelepipedal, has vegetal decoration. They are somewhat reminiscent of certain capitals of the Great Mosques of Cordoba and Tlemcen. In the other capitals a central palmette decoration rests on caulicoli springing from the acanthus leaves on the lower part. Already present in the ornamental vocabulary of the Visigoths, caulicoli appear in Western Islamic art in the Aljaferia of Saragossa.

The brick minaret composed of a tower and a lantern-turret occupies the south-eastern corner of the edifice. The upper platform can be reached by a staircase winding around a central core. Its four sides are decorated with a series of rectangular panels, some adorned with curvilinear lozenge patterns, others with cusped arches. On each of the four sides of the lantern-turret a cusped arch fits into the inner frame. Ceramic mosaic adds a touch of colour to the overall decoration. This decoration, which is typical of Almohad minarets, appears for the first time in the lantern-turret of the Kutubiyya mosque in Marrakech, and is a major element in the Mosque of Hasan in Rabat, the Giralda Mosque in Seville and above all the Qasaba Mosque in Marrakech.

Of all the monuments in Tlemcen, the Sayyidī Abū al-Hasan Mosque is the one that most closely resembles the great Moroccan and Spanish monuments.