large open plain on the northern side for providing water supplies from the proposed storage behind the Satpula, to grow irrigated crops to sustain a large population. Thus, a reliable water storage reservoir in the arid region of Delhi, which has the Thar desert on its west, was built as the headworks or weir across the Barapulla Nallah. Even though no epigraphic evidence is available to date the Satpula, a reasseacrh study report has conjectured that it could be dated to the same time as the four–eyyan Mosque (first of its kind in India) called Jami built by Muhammad bin Tughluq in 1343. Structure The Satpula across the stream was built as a gate controlled weir. The total length of the structure is . It has been constructed in stone masonry. The eleven bays of the weir controlled by sluice gates cover a total length of . These eleven bays consist of eleven water tunnels (sluices), each in length, in height, and in width. These are located at different levels, with seven main bays at the lowest level. The balance two additional bays on each bank, on the far east and west sides, are at a higher level. The control arrangements seen now are in the form of gate grooves to operate vertical slide gates. When built, wooden vertical sluice gates made of heavy boards of size in thickness, width, and more than in height, were operated by a rope and pulley arrangement to control flow of water; the wooden gates have since disintegrated but the gate groves are visible in each bay. The gates of the sluices were closed as a defensive measure against possible attack in the dry season when no storage remained in the dam. Each bay of the weir has an arched opening. On both banks of the weir identical towers (defensive bastions, projecting on the south and north sides) of diameter, but with octagonal shape chambers, are built, which once functioned as madrasa (Islamic school of learning). Hence, the Satpula is also known as "Madarsa". The second level sluice bays on both banks lead to arched corridors. The walls of the octagonal chambers have graceful decorations. The stream tapped by this weir, has been diverted now further east. The indication of the use of the sluices of the structure, either as a dam or for defense purposes, could be gauged from the platforms provided at