Mysterious iron pillar out in the open confounds scientists as it hasn't rusted in 1,600 years

From the Leaning Tower of Pisa to the pyramids of Egypt and Stonehenge, some monuments are architectural marvels that have remained mysterious for centuries. The question most people and researchers continue to ask is how such structures were built when technology was much less advanced than it is now. One such monument is a 1600-year-old iron pillar in Delhi, India, which has been in the spotlight because it hasn't rusted even after being exposed to diverse weather conditions including rain and extreme heat. Researchers wonder what might have gone behind the creation of this pillar in the Qutb Minar Complex that attracts visitors from across the globe. The decorative pillar has survived both harsh climate and pollution without rusting like usual things made of iron and wrought iron as per CNN.

Some special structures, like the Eiffel Tower in Paris, are protected by a special paint, but the same is not true for this pillar. Scientists all around the world had been trying to crack the mystery behind this pillar since 1912, until researchers from the Indian Institute of Technology in Kanpur, India finally found the reason behind the pillar's remarkable ability to stay rust-free. It was revealed that, unlike modern iron, the pillar doesn't have sulfur and magnesium, but instead it has a high quantity of phosphorous.

Another reason behind the iron pillar's extraordinary quality is the method used for making it. It was created through forge welding, which entails heating and hammering the iron to maintain its phosphorous content, something that isn't done anymore. A thin layer of a material called misawite was found on the iron pillar's surface as per Archeo-metallurgist R. Balasubramaniam, author of the report. The compound made of iron, hydrogen, and oxygen adds to the pillar's strength. As per the study, this layer was formed by reactions taking place due to the pillar's phosphorous content.

Balasbraniam believed that the ancient craftsmen understood phosphorous's ability to create a rust-resistant layer on iron and thus chose iron ore with high phosphorous content intentionally, as per Britannica. There's also another theory that says that the lack of rust formation on the iron pillar might be due to Delhi's lack of humidity and the climatic conditions that the pillar has been in. However, these tests were conducted from 1930 to 1960, which isn't enough to calculate the different climatic conditions the pillar has been exposed to. This theory also raises questions about the original location of the pillar, which isn't known for sure.

Some researchers believe that the pillar was originally placed at Varah Temple of Udayagiri Caves, near Vidisha in Madhya Pradesh, and was created under the Gupta Empire in the 4th century or 5th century BC. Another theory states that the pillar was created by the astronomer Varahmira who brought it from Vidisha to Mehrauli with him, where it's currently located. It is believed that the pillar's property might help create corrosion-resistant iron for future use. “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,” Pragya Nagar, conservation architect, and heritage expert, told CNN.