The Sion Hillock Fort is a fort in Mumbai (Bombay), India. It was built by the British Governor of Bombay Gerard Aungier atop a conical hillock. The hillock is situated a few metres from the Sion railway station. Sion was the boundary between British-held Parel island and Portuguese held Salsette Island and the castle marked the northeast boundary of their possession. The fort was built between 1669 and 1677.
The fort is dilapidated and a collection of broken stone steps, scattered walls and ruins, overrun by trees and ground cover. The fort wall has a small room on top. A series of pathways lead to it.
The fort offers a panoramic view, overlooking the salt pans in the Thane Creek. However vandalism and apathy have taken toll on the structure.