Rust helped protect Delhi’s iron pillar for roughly 1,600 years. Research on its surface found that the iron’s chemistry helped form a compact corrosion barrier. Modern weathering steel also uses a protective surface: the New River Gorge Bridge in West Virginia and Idaho’s Perrine Bridge are examples. The modern alloy is different from the ancient pillar’s iron; no historical technology transfer is claimed.

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Rust helped protect this iron pillar for roughly sixteen hundred years. It still stands in Delhi. Scientists examining its surface found the explanation: the iron’s chemistry helped form a compact rust barrier that slowed further corrosion. Modern engineers also put protective rust to work. West Virginia’s New River Gorge Bridge and Idaho’s Perrine Bridge use weathering steel. It develops a protective surface that reduces the need for painting enormous steel structures. This pillar has been demonstrating the principle for sixteen hundred years.