The Great Al-Omari Mosque was built in 1291 by Mamluk Sultan al-Mansur Qalawun atop a Crusader fortification and church that included a refectory, stables and rooms for the knights Templar. The complex is expansive and was the largest and most important mosque in the city prior to the construction of the Hariri mosque in 2003 on Saida’s northern fringes. The interior is impressive, with a 10-meter high ceiling that is held by study external buttressing from the Crusader era. The mosque was renovated repeatedly at the end of the 19th century, and was partially destroyed by Israeli bombardment during the Invasion of Lebanon in 1982. Since then, it has been rebuilt in 1986 using traditional construction techniques and the remains of the same stones on site. The renovation project received the Aga Khan Award for Architecture in the 1987-1989 Cycle.

The mosque is longitudinal and oriented along an east-west axis which suggests that it had previously been a church built in the neo-byzantine style. Once it was converted to a mosque in 1291, a minbar was added on the southern façade, shifting the primary orientation of the building towards the north-south axis. Over time, an external courtyard and accessory prayer halls were added on the north side, as well as a series of ablution rooms, a school, and a minaret that dates from the late Ottoman period.