The Iron Pillar of Delhi is an ancient monument located in the Qutb complex in Delhi, India. It is a 7.21 m high pillar made of iron, dating back to the 4th century AD. The pillar is notable for the rust-resistant composition of the metals used in
From Wikipedia
The iron pillar of Delhi is a metal structure 7.21 metres high with a 41-centimetre (16 in) diameter that was constructed by Chandragupta II, and now stands in the Qutb complex at Mehrauli in Delhi, India.