This chapter explores the making of Sofia as an Ottoman city. The central thread in the narrative is the functioning of the system of pious foundations, which played the most decisive role in the expansion and transformation of the built fabric and the provisioning of public services. The main theme is the city’s relationship with the natural environment and the construction, functioning, and maintenance of its water supply system. The chapter specifically aims at bringing attention to the fact that the upsurge of building activity and the Ottomanization of the built environment that were experienced since the mid-fifteenth century, and especially in the sixteenth century, were accompanied by the establishment of a water infrastructure. Yahya Pasha’s water supply system was established at the turn of the sixteenth century, the beginning of a period that witnessed the biggest advances of the Ottomans both in the construction of water facilities and in the institutionalization of water management. Chronologically, the narrative encompasses the entire early modern period in Sofia’s history, shedding light on Ottoman water supply both in terms of its technical aspects and in terms of the role that it played in the construction of the local eco-community.