Already before 1571, when the designing and procuring of building materials for her mosque complex began, Nurbanu had planned to establish a vakıf, a perpetual charitable endowment to support the construction and maintenance of the buildings. Such endowments had tied (and held) together economic, religious, social and cultural life in the Ottoman Empire since its inception, following Byzantine, Arab and Seljuk models. The sultan who conquered Constantinople, Mehmed II (r. 1444–1446, 1451–1481), very well understood the utility of endowments for urban development, establishing two of the largest evkaf in the entire empire, one in his own name, the other in that of the Hagia Sophia. At the same time, he urged officials and dignitaries of his court to do the same and to construct buildings with commercial, social and religious purposes. That the resulting mosque complexes provided durable focal points for urban development is still evident in those neighbourhoods that carry the mosque founder's name – such as Davutpaşa or Mahmutpaşa. The building complexes provided an urban infrastructure in the form of water supply, roads and canalisation; employment opportunities through their hiring of personnel; business opportunities through the creation of market space, baths and inns; and social and cultural facilities in the form of schools, convents, public kitchens and hospitals. Although the foundation's income was not subject to taxes and therefore promised no profit for the state's coffers, endowed complexes had other advantages for governing Ottoman subjects.