CNN
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Can an iron structure stand tall for 1,600 years without rusting, despite being exposed to the elements?
It seems implausible, considering the supposed lack of technology at the time of its construction.
Yet, inside New Delhi’s UNESCO-listed Qutb Minar complex – a collection of historic monuments and buildings built in the early 13th century in the city’s southern Mehrauli district – one mysterious structure stands as a testament to this very enigma.
Visitors to the courtyard of the complex’s Quwwat-ul-Islam Mosque will immediately spot an imposing 7.2-meter, six-ton iron pillar with a decorative top that’s even older than the complex.
Remarkably, the pillar is now as pristine as the day it was forged, defying both age and environmental adversities, including the Indian capital’s intense temperatures and increasing pollution. Dating back to the 5th century, its remarkable resilience continues to captivate travelers today.
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The Quwwat-ul-Islam mosque is part of the UNESCO-listed Qutb Minar complex.
Typically, iron and iron alloy structures exposed to the air or moisture oxidize over time, rendering them coated in rust unless they are protected, like the Eiffel Tower, by layers of special paint. Scientists both in India and abroad began studying the iron pillar in Delhi in 1912 to try to figure out why it hadn’t corroded.
It wasn’t until 2003 that experts at the Indian Institute of Technology (IIT) in the northern city of Kanpur cracked the mystery, revealing the answer in the journal Current Science.
They found that the pillar, primarily made of wrought iron, has a high phosphorus content (about 1%), and lacks sulfur and magnesium, unlike modern iron. Additionally, ancient craftsmen used a technique called “forge-welding.”
That means they heated and hammered the iron, keeping the high phosphorus content intact, a method uncommon in modern practices.
Archeo-metallurgist R. Balasubramaniam, who authored the report, said that this unconventional approach contributed to the pillar’s enduring strength.
A thin layer of “misawite,” a compound of iron, oxygen and hydrogen, was also found on the pillar’s surface, he said. This layer is formed catalytically by the presence of high phosphorus in the iron and the absence of lime, thus further enhancing the pillar’s durability.
Balasubramaniam lauded the metallurgists for their ingenuity, describing the pillar as “a living testament to India’s ancient metallurgical prowess.”
Its durability is evidenced by historical accounts, including an incident in the 18th century when a cannonball fired at the pillar reportedly failed to break it, showcasing the impressive strength of this ancient monument.
Today, the pillar serves as the emblem of scientific organizations like the National Metallurgical Laboratory and the Indian Institute of Metals.
Myths and legends surround pillar’s origin
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A closeup of the inscription on the Iron Pillar.
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