An important factor in the development of Cairo's economic center was the growing number of "waqf" institutions, especially during the Mamluk period. Waqfs were charitable trusts under Islamic law which set out the function, operations, and funding sources of the many religious/civic establishments built by the ruling elite. These funding sources often included the revenues of designated shops or other commercial establishments. Among the early and important examples of this institution in Cairo's center was the complex of Sultan Qalawun (which included a madrasa, hospital, and mausoleum), built in 1284-85. A part of the complex's revenues came from a nearby "qaysariyya" (a bazaar or market complex made up of rows of shops) built in front of the Ayyubid-era madrasa of al-Salih (whose minaret is still visible today behind these rows of shops). This qaysariyya was thus an early prominent example of the purpose-built commercial structures erected in Cairo under the Mamluks as part of a waqf. In this case, the complex fronted the main street on one side while other shops were reached by an inner alley.