Patron and founder: Sultan Hasan  Illuminated frontispiece from the Qur'an commissioned by sultan Al-Hasan for his complex. This manuscript is part of the National Library of Egypt's Collection of Mamluk Qur'an Manuscripts inscribed in the UNESCO Memory of the World Register

Sultan al-Nasir Hasan (full name: An-Nasir Badr ad-Din Hasan ibn Muhammad ibn Qalawun) ascended the throne at the age of 13 in 748 AH/1347 CE.[1] When he reached maturity in 1350, he arrested the Emir Manjaq who controlled all of the state's affairs. Prior to that arrest, the emir was restricted to an allowance of just one hundred dirham per day. This pocket change was collected by servants for the Sultan. It's especially striking considering that during that time, the emir Shaykhu was estimated to have an income of 200,000 dirham per day. This deprivation may be viewed as a prompt for his later extravagance. Upon taking over the reins, Sultan Hasan placed people of his own favor into positions of power. This happened at the expense of dignitaries currently in position; it upset many of them. Discontented Emirs arrested the Sultan in 1351, held him in jail for three years, and promoted his brother as-Salih Salih to the throne. Hasan spent his time in jail studying and his obituaries commented on his learning as a result.[1] He returned to power and again reshuffled the ruling establishment attempting to solidify power, but Sultan Hasan was assassinated by his commander in chief of the army, Yalbugha al-Umari, a Mamluk thought to be loyal.[1] Because of the Sultan's extravagance in spending fortunes on women and other forms of favoritism, the commander rebelled against the Sultan. A contemporary Syrian historian, Ibn Kathir, backed this reputation.[1] Ibn Kathir blamed the sultan for his greed and squandering of public funds. The lavish expenses noted coincide with the Sultan's extensive mosque. After his assassination in 1361, Sultan Hasan's body was never found; the mausoleum never served its purpose.[2]

Construction  View of Sultan Hasan's mosque and of Rumayla Square in 1880.

The mosque's construction is considered all the more remarkable as it coincided with the devastation wrought by the Black Plague, which struck Cairo repeatedly from the mid-14th century onwards.[3][1] Its construction began in 1356 CE (757 AH) and work proceeded for three years "without even a single day of idleness".[4] In fact, work appears to have continued even up to 1363, even after Sultan Hasan's death, before eventually ceasing.[1] An inscription on the mosque notes the name of amir Muhammad ibn Biylik al-Muhsini as the supervisor of the construction of the mosque. Unusually, his name was placed near Sultan Hasan's in the inscription, which demonstrates how important the undertaking of the project must have been.[1] The amir's high standing otherwise was another indication of this prestige, as he was appointed governor of Cairo in 1330 and oversaw other construction projects including the renovation of the hippodrome established by al-Zahir Baybars near the Citadel.

The most substantial available source concerning the mosque's construction is al-Maqrizi, writing six decades afterwards, as he had access to administrative documents that are unavailable to historians today. The manual labour needed for construction must have been partly depleted by the ongoing ravages of the plague, yet this does not appear to have been the main challenge. Maqrizi mentions that the construction of the mosque cost 30,000 dirham every day.[4] The total construction costs amounted to over one million dinars, making it the most expensive mosque in medieval Cairo.[1] Even the Sultan is said to have become discouraged at times by the cost of the project. Financing for the mosque was made possible by a few factors: first, the austerity measures implemented by Manjaq, one of the amirs in charge of state affairs before Sultan Hasan reached maturity; secondly, the influx of wealth to the state caused by the plague-related deaths of many Mamluk amirs whose properties were subsequently transferred to the state treasury, including the enormous wealth of amir Shaykhu; and thirdly, through extortion of the sultan's subjects during his reign.[1]

The importance and scale of the building project also attracted craftsmen from all over the Mamluk empire, including the far-away provinces of Anatolia, which may explain the diversity and innovativeness of the mosque's design and decoration.[1] It is also believed that limestone from the Pyramids of Giza was quarried for use in the mosque's construction.[5][6][7]

Later events  The mosque-madrasa-mausoleum of Sultan Hasan today, as seen from the Citadel. (The other large mosque on the right is the al-Rif'ai Mosque.)

Due to the mosque's location near the Citadel and because of its massive and sturdy construction, it was used on more than one occasion as a fortified position or as a platform from which to launch attacks on the Citadel. Al-Maqrizi, noted that "as soon as there occurred strife between the people the state, a number of amirs and others ascended to the top of the mosque and began to bombard the Citadel from there".[4] This, in turn, persuaded more than one sultan to order the mosque to be demolished or blocked up. In 1391, rebel amirs against Sultan Barquq mounted the roof of the mosque and launched projectiles at the Citadel, provoking the sultan into ordering the stairs and platform of the entrance destroyed and the doorway boarded up.[8] In 1500, Sultan Janbalat, anticipating another rebel attack from the mosque, ordered it demolished; however, after three days of unsuccessful demolition attempts on the mosque's southeastern (Citadel-facing) walls, he was forced to give up.[1] In 1517, the very last Mamluk sultan, Tumanbay, took refuge inside the mosque in an attempt to evade capture by the victorious Ottoman army as it took control of Cairo, resulting in the Ottomans bombarding the mosque with cannonballs from the Citadel. In 1660, chronicles described the mausoleum's dome as still being full of holes made by cannonballs.[8] Even in the 18th century, during the period of Ottoman control, the mosque was apparently closed for many years after unrest in 1736, and was only reopened in 1786 by order of Salim Agha.[3] Some of these demolition attempts, however, drew criticism from Cairo's population and authorities were often subsequently pressured into repairing damages.[1]

In 1659, the northern minaret attached to the mausoleum collapsed. In 1671-1672, the minaret was replaced with a smaller one, with a slightly different form, and at same time the original wooden dome of the mausoleum was replaced with the current dome, also in a different shape from the original.[1][8]

In 1869, construction began on a monumental new mosque, the Mosque of ar-Rifa'i, right next to the existing mosque of Sultan Hasan. Completed in 1912, its size is comparable to Sultan Hasan's construction and it was built in a neo-Mamluk style. The two buildings together now dominate the old Rumayla Square (now renamed Midan Salah ad-Din) across from the Citadel.[8]