The Riwa Fort (also Rewah Fort), locally known as Kala Qilla or Black Fort, is a fort in central Mumbai (Bombay), India on the banks of the Mithi River. The fort is currently in a dilapidated condition amidst the Dharavi slums. It was built by the first governor of Bombay, Gerald Aungier (1669–1677). It was part of the larger Bombay Castle, and marked the northern portion of British-held Bombay in the 17th century. The castle was also used as a watchtower, guarding the territory against the Portuguese-held (and later Maratha-held) Salsette Island.