Megalithic monuments are among the earliest and most permanent of archaeological structures, and so many of them were used, or more properly, have been used and reused for thousands of years. Their original intent is likely lost to the ages, but they may have had multiple functions as they were used by different cultural groups over the centuries and millennia.

The Jantar Mantar is an equinoctial sundial, consisting of a gigantic triangular gnomon with the hypotenuse parallel to the Earth’s axis. On either side of the gnomon is a quadrant of a circle, parallel to the plane of the equator. The instrument is intended to measure the time of day, correct to half a second and declination of the Sun and the other heavenly bodies.