One of the holiest sites in Egypt, the mosque was originally built by the Fatimids in the 12th century as a shrine and is said to contain the head of Husayn, the Prophet's grandson. Al-Husayn is the spiritual heart of the Islamic city. It is here that the president and his ministers come to pray on important religious occasions. Many of the Sufi orders in the neighborhood perform Friday prayers at al-Husayn. During the mulid (celebration) of al-Husayn, held during the Muslim month of Rabi'a al-Akhiri (the fourth month in the Muslim calendar), the square in front of the mosque becomes a carnival. During Ramadan, the area is packed with people from sunset to dawn.
Not only was Husayn the grandson of the Prophet, but he was also the son of 'Ali, the fourth caliph and cousin of the Prophet. A group of followers who believed that 'Ali and his descendants should lead the faithful broke ranks with the majority (known as the Sunnis) when the Ummayads took control of the umma
(the Islamic nation). This group became known as "the group of 'Ali" or Shi'a 'Ali, later Shi'a for short. Husayn is greatly revered by the Shi'a for his role as a martyr to the cause when, in 680, he and a band of his followers were massacred at the battle of Kerbala in Iraq.
If it seems strange that the head of a Shi'a martyr be given such importance in a country that is overwhelmingly Sunni, it should be noted that the Fatimids, the original builders of al-Qahira, were Shi'a. The 200 years in which they ruled the city left an impact on the traditions of the people. Not only did the Shi'a found the most prestigious Islamic university, al-Azhar, but they also were responsible for inculcating in the populace a veneration for saints, holy men, or relatives of the Prophet—a practice not at all in keeping with a strict interpretation of Sunni Islam. Thus, although the head of Husayn was brought to Cairo for safekeeping by a ruling minority, the Sunni majority quickly accepted the shrine as part of its heritage.
The mosque itself is a 19th-century stone building heavily influenced by the Gothic Revival; only elements of older structures remain. On the south end of the southeast facade stands a partial wall with a gate, known as Bab al-Akhdar (the Green Gate), which probably dates from the Fatimid dynasty. Inside the mosque, past the main prayer hall, is the Tomb of Husayn, a domed chamber built by 'Abd al-Rahman Katkhuda in the 1760s. The grave is enclosed with a silver mashrabiyya screen.
The mosque is technically closed to non-Muslims. However, while large tour groups are not allowed to enter, there is more leeway for the individual traveler, provided that you avoid prayer times (the hour around noon; 1 pm between April and October during daylight saving time) and Fridays. Women should cover their heads and everyone should cover shoulders and knees.