The Iron Pillar (also known as the Ashokan Pillar) of Delhi, India. It is a 7 m (23 ft) high pillar in the Qutb complex, notable for the composition of the metals used in its construction.
Scholars attribute the creation of the pillar, weighing more than six tons, to the era of Chandragupta Vikramaditya (375–413) of the Gupta Empire. Although some suggest earlier dates as early as 912 BCE. Initially, the pillar stood at the center of a Jain temple complex containing twenty-seven temples. However, Qutb-ud-din Aybak destroyed these temples. He utilized their materials in constructing the Quwwat-ul-Islam mosque and the Qutub Minar complex, where the pillar remains today.
Archaeologists and metallurgists have been drawn to the pillar. Which they deem “a testament to the skill of ancient Indian blacksmiths.” Its remarkable corrosion resistance is attributed, to both the Delhi environment and the high phosphorus content in the iron. Which forms a protective layer of crystalline iron hydrogen phosphate.
About the Iron Pillar
Crafted in a single forge, artisans constructed an iron pillar weighing over 6 tonnes and standing more than 7 meters tall atop the Vishnupada hill, located somewhere in modern central India. It bears Sanskrit inscriptions in the Brahmi script detailing the achievements of the great Gupta ruler Chandragupta Vikramaditya.
More than 1600 years ago, building an iron pillar of this huge size in a single forge itself is an indication of the advanced metallurgy of the ancient Indians. Even in today’s modern technological world, it is a great achievement to forge such a huge pillar in a single forge!!!
But there’s more, this pillar which contains more than 98% pure iron, even after 1600 years has not caught rust!!! It is 100% corrosion-resistant in spite of the fact that it is 98% iron!! This indicates one of the great technological achievements of the ancient Indians. Even today it is next to impossible to construct such a huge corrosion-resistant iron pillar. Corrosion-resistant technologists from all over the world have studied this pillar.
Modern-day technology uses limestone in blast furnaces. which carries away most of the phosphorus content in the ore in the form of slag. Ancient Indians instead by solid state reduction (used charcoal as a reducing agent) to extract pure iron with low carbon content from the ore.
One of the research opinions about the iron pillar’s corrosion-resistant nature is that the high amount of phosphorous. It has formed a thin protective layer on the surface of the pillar. Thereby making it corrosion-proof. Since other ancient iron works of the same period do not contain such a high quantity of phosphorous. This indicates that blacksmiths intentionally added extra phosphorous to the iron pillar.
Another theory proposes that the relatively low humidity of Delhi prevents the Iron pillar from corroding. However, I strongly disagree with this theory and emphasize it. It is not Delhi’s climate but the composition of the pillar itself that accounts for its corrosion-resistant nature. I reinforce this belief based on my observation of a similar ancient corrosion-resistant Iron pillar during a trek to the Kodachadri hills on the west coast of South India. Additionally, I’ve heard of a similar corrosion-resistant Iron pillar in the Konark temple of Orissa. Both locations experience high humidity year-round, yet their iron pillars remain corrosion-resistant. The widespread presence of such pillars across India suggests that the Iron Pillar of Delhi was not an isolated instance of ancient ingenuity. It reflected common technical knowledge shared by the ancient civilization of this country.