This mysterious iron pillar in India has been exposed to the elements for over 1,600 years. So why hasn’t it ever rusted?

By Poonam Binayak, CNN

(CNN) — 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.

How has it defied corrosion for so long?

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

Beyond its metallurgical intrigue, the origin of the Iron Pillar is also veiled in mystery. One widely circulated account traces it back to the Gupta Empire, particularly under the reign of Chandragupta II, also known as Vikramaditya, around the 4th and 5th centuries.

According to this tale, the pillar was erected in the Varah Temple of Udayagiri Caves, near Vidisha in Madhya Pradesh, as a victory monument dedicated to the Hindu deity Lord Vishnu. It’s said to have once borne a statue of Garuda, the mythical eagle mount of Vishnu, on its top, though this figure has been lost to history.

Another theory, proposed by heritage activist and educator Vikramjit Singh Rooprai, suggests it may have been bought by Varāhamihira, a renowned astronomer in the court of King Vikramaditya.

“One of his books, the ‘Surya Siddhanta,’ details methods for calculating celestial positions, eclipses, and other astronomical phenomena – and it is believed that he used a tall pillar in his calculations,” says Vikramjit.

“Therefore, upon his migration from Vidisha to Mihirapuri (now Mehrauli), where he founded an observatory, there exists a likelihood that he brought the pillar with him for continued use in his studies and calculations.”

Additionally, some historical records credit notable figures like Raja Anangpal of the Tomar dynasty, and Muslim rulers such as Iltutmish and Qutbuddin Aibek, for the relocation of the pillar to the Qutb complex.

It’s also been mentioned in the arts. In the epic poem “Prithviraj Raso,” penned by Chand Bardai, a courtier in the Chahamana dynasty under King Prithviraj Chauhan, the Iron Pillar holds great significance.

“Bardai describes the Iron Pillar in Raso as a nail holding the Earth on the hoof of Sheshnag, the serpent king in Hindu mythology,” says Vikramjit.

“Raso recounts how Raja Anangpal tried to uproot this nail despite warnings from Brahmins of dire consequences. When it was pulled out, revealing a red base believed to be Sheshnag’s blood, panic ensued, fearing Earth’s destruction. Anangpal quickly ordered its reinstallation, but it was not properly secured, resulting in it becoming loose. Thus, Bardai suggests that this incident inspired the colloquial name ‘Dilli’ for Delhi, which is a pun on the word ‘dhilli’, meaning ‘loose’ in Hindi.”

Cultural significance and preservation efforts

According to one legend, if you stand with your back against the pillar and wrap your arms around it, making sure your fingers touch each other, your wish will come true – a tradition that imbues the pillar with spiritual significance beyond its historical value.

However, the ASI (Archeological Survey of India) has put a fence around the pillar to minimize human impact.

Conservation architect and heritage expert, Pragya Nagar, finds the pillar’s preservation remarkable within the complex, despite the demolition and reconstruction of its surroundings over the years.

“If we do look at the technique that was used to create the pillar from a fresh perspective, beyond mere acknowledgment of its ancient origins, we may discover avenues to leverage similar methods for the development of sustainable material alternatives, considering the environmental harm associated with processes like metal extraction,” she tells CNN.

“It is imperative to look at history beyond relics and monuments that simply need to be conserved and marveled at, but as repositories of traditional knowledge and indigenous practices. This holistic approach has the potential to pave the way towards a more sustainable future.”

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