Iron pillar of Delhi

The Iron Pillar located in Delhi, India, is a 7 m (23 ft) column in the Qutb complex, notable for the rust-resistant composition of the metals used in its construction.

The pillar has attracted the attention of archaeologists and materials scientists because of its high resistance to corrosion, and has been called a "testimony to the high level of skill achieved by the ancient Indian iron smiths in the extraction and processing of iron." The corrosion resistance results from an even layer of crystalline iron hydrogen phosphate hydrate forming on the high phosphorus content iron, which serves to protect it from the effects of the local Delhi climate.

The pillar weighs over 6,000 kg (13,000 lb), and is thought to have originally been erected in what is now Udayagiri by one of the Gupta monarchs in approximately 402 CE, though the precise date and location are a matter of dispute.

The height of the pillar, from the top of its capital to the bottom of its base, is 7.21 m (23 ft 8 in), 1.12 m (3 ft 8 in) of which is below ground. Its bell pattern capital is 1.07 m (3 ft 6 in) in height, and its bulb-shaped base is 0.71 m (2 ft 4 in) high. The base rests on a grid of iron bars soldered with lead into the upper layer of the dressed stone pavement. The pillar's lower diameter is 420 mm (17 in), and its upper diameter 306 mm (12 in). It is estimated to weigh more than six tonnes (13,228 lb).

A fence was erected around the pillar in 1997 in response to damage caused by visitors. There is a popular tradition that it was considered good luck if one could stand with one's back to the pillar and make one's hands meet behind it. The practice led to significant wear and visible discolouration on the lower portion of the pillar.

The pillar carries a number of inscriptions and graffiti of different dates, some of which have not been studied systematically despite the pillar's prominent location and easy access.

The oldest inscription on the pillar is that of a king named Chandra (IAST: Candra), generally identified as the Gupta emperor Chandragupta II.

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