There’s a 1,600-year-old iron pillar
in the middle of Delhi
that has never rusted.
Why?

Question

Accepted Answer

A thin oxide layer + high phosphorus content in the iron creates a protective film. — Gupta-era metallurgists knew alloys we’re still studying. The Qutb complex pillar is 98% pure iron. It shames modern steel.

There’s a 1,600-year-old iron pillar in the middle of Delhi that has never rusted. Why?