Iron Pillar

The Iron Pillar was originally established in 402 AD in the front courtyard facing the Vishnu Temple as a 'Vishnudhwaja' which is in honour of Lord Vishnu atop Vishnupada, a small hillock at Udayagiri in Madhya Pradesh by Chandra Gupta II who ruled between 375 CE and 414 CE.

It was later moved by Sultan Iltutmish in 1233 AD from its original location to where it stands today within the Qutb Complex in South Delhi. The 'Iron pillar of Delhi is 23 feet 8 inches high (7.2 metres) with 16 inches diameter structure.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(III) hydrogen phosphate hydrate forming on the high-phosphorus-content iron, which serves to protect it from the effects of the Delhi climate.