The iron pillar in Delhi's Qutb complex stands over seven metres tall and dates to around 400 CE. It has survived centuries of monsoons with very little rust. The secret is a thin protective layer on its surface.
Truth label: Established. Strong evidence and broad agreement among experts.
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The chemistry
The iron is rich in phosphorus. It helped form a thin, stable film that blocks further rusting.
Forged, not cast
It was hammered together from hot lumps of iron, an enormous task for the time.
Learn
- A royal record. An inscription in Sanskrit honours a king, usually identified as Chandragupta II.
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What protects the Delhi pillar from rust?
A thin protective film. Phosphorus-rich iron formed a protective layer.
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