The Mystery of the Mehrauli Iron Pillar

The iron pillar is incredibly old. It was built around 1,600 years ago during the Gupta Empire. According to the ancient Sanskrit inscriptions carved on the pillar, it was erected in honor of the Hindu God Lord Vishnu, and to celebrate the military victories of a powerful king named 'Chandra' (widely believed by historians to be the great Emperor Chandragupta II).

What makes this pillar world-famous is its metallurgy. The pillar is made of 98% pure wrought iron and is completely exposed to the harsh Delhi weather (rain, heat, and pollution). Normally, iron rusts and crumbles away in a few years when exposed to moisture.

However, this pillar has not rusted even after 1,600 years.

Scientists discovered that ancient Indian blacksmiths used a brilliant technique. They coated the iron with a thin layer of 'misawite' (a compound of iron, oxygen, and phosphorus). The high phosphorus content in ancient Indian iron forms a protective film over the pillar, preventing the metal from rusting.