The Mosque of El Aqmar locates in El Muiz Le Din Allah Street few meters away from the Sabil-Kuttab of Abd El Rahman Katkhuda . Some inscriptions in the mosque highlight that it was established by El-Mamoun El-Bataihi who served as the Wazir or Minister of the Caliph El-Amer Bi-Ahkam Allah for about four years.
El-Mamoun is described there as the commander of the armies and the sword of Islam. The mosque is one of the prominent mosques in Cairo due to its unique style of decoration that is affected by the Ismaili Shiite Mazhab adopted by the Fatimids at that time. This appears obviously in the inscriptions of the names of Prophet Mohammed and Ali, the Shiite claimed descendent, in the niches over the façade. These inscriptions are designed in that way to illuminate some of the Shiite believes concerning the matter of the members of the Prophet's family and his descendents. Of special interest in this mosque is the design of the façade and the entrance: the stone façade parallels the street and the entrance is not facing the Qibla wall unlike most of the buildings that were established before. The entrance is handsomely decorated with identical wings on its either sides that were gifted to the mosque by the Bohara community.
The most distinguishing features in that building are the pierced medallions over the entrance and the shells and the stalactite- panels that beautify the niches because these ornaments were not commonly used before. The door of El-Aqmar mosque is a good example for the doors of the mosque at that time since it was supplied with a place for keeping the books of Holy Quran in its back. From inside, the central courtyard of the mosque is handsomely ornamented with original Kufic inscriptions for some Quran verses. In the late 14th century Emir Yalbugha El-Salami gifted the Mihrab, the Minbar and the Ablution fountain to the mosque. By the passage of time the mosque became under the street level, yet it is still preserved due to the numerous processes of restoration of it. The present windows and marble patterns in the sanctuary area and the Minaret's stump date back to a later processes of restoration.
You can get more information here.