The pillar is 7.2 m high and weighs 6 tons and remains intact despite being exposed to sun and rain for the past 1,600 years.
Inside New Delhi’s Qutb Minar, a complex of monuments and historic buildings built in the early 13th century in the city’s southern Mehrauli district, visitors can find a 7.2 meter high iron column, weighing 6 tons in the courtyard of the Quwwat-ul-Islam mosque, according to CNN. The 5th century pillar has defied the times as environmental conditions, including high temperatures and pollution, have increased in the Indian capital.
Normally, structures made of iron and iron alloys exposed to air or moisture oxidize over time and become covered with a layer of rust unless protected with a special paint layer like the Eiffel Tower. Scientists both inside and outside India began studying the iron pillar in 1912 to find out why it did not corrode. It was not until 2003 that experts at the Indian Institute of Technology (IIT) in Kanpur city were able to explain the mystery and give the answer in Current Science magazine.
They found that the pillar was mainly made from wrought iron containing high amounts of phosphorus (about 1%) and no sulfur or magnesium, unlike modern iron. Additionally, ancient craftsmen used a technique called “forge welding”. That means they heated the iron and hammered it, which kept the high phosphorus levels intact. This non-traditional method contributes to the durability of the pillar, said R. Balasubramaniam, a paleometallurgist and study author.
A thin layer of misawite, a compound of iron, oxygen and hydrogen, was also found on the surface of the pillar. This layer is formed through catalysis with high levels of phosphorus in iron, thereby enhancing the durability of the pillar. Balasubramaniam praised the metallurgists’ creativity, describing the pillar as “living proof of India’s ability to forge iron in ancient times”.
The origin of the iron pillar is also another mystery. A widely circulated record states that the pillar was born during the Gupta empire, during the reign of Chandragupta II, also known as Vikramaditya, around the 4th and 5th centuries. According to the story, the pillar was built at the Varah temple in the Udayagiri caves, near Vidisha in Madhya Pradesh, as a victory monument to Lord Vishnu. The pillar once had a statue of Garuda, the mount of Lord Vishnu, at the top, but the statue has disappeared with history.
Today, the pillar serves as the symbol of scientific institutions such as the National Metallurgical Laboratory and the Indian Institute of Metals. However, ASI (Archaeological Survey of India) built a moat around the iron pillar to minimize human impact.