The iron pillar is one of the worlds foremost metallurgical curiosities. The pillar, almost seven metres high and weighing more than six tonnes, was erected by Chandragupta II Vikramaditya (375 AD-414 AD), (interpretation based on careful analysis of archer type Gupta gold coins) of the Gupta dynasty that ruled northern India 320-540. The pillar with the idol of Garuda at the top was originally located at a place called Vishnupadagiri (meaning Vishnu-footprint-hill). This place has been identified as modern Udayagiri, situated in the close vicinity of Besnagar, Vidisha and Sanchi. These towns are located about 50 kilometres east of Bhopal, in central India. There are several aspects to the original erection site of the pillar at Udayagiri. It must be worth noting that Vishnupadagiri is located on the Tropic of Cancer and, therefore, was a centre of astronomical studies during the Gupta period. The Iron Pillar served an important astronomical function, when it was originally at Vishnupadagiri. The early morning shadow of the Iron Pillar fell in the direction of the foot of Anantasayain Vishnu (in one of the panels at Udayagiri) only in the time around summer solstice (June 21). The creation and development of the Udayagiri site appears to have been clearly guided by a highly developed astronomical knowledge. Therefore, the Udayagiri site, in general, and the Iron Pillar location in particular, provide firm evidence for the astronomical knowledge that existed in ancient India around 400 AD.