To this day, the Delhi Pillar remains a “living testament” to the mastery of metallurgists in ancient India .

The Delhi Pillar is one of the famous ancient monuments of India.  Delhi is an iron pillar cast in the 5th century, erected by King Kumara Gupta I of the Gupta dynasty, who ruled northern India from 320-540.

Originally this pillar was part of the Muttra Temple, with a Garuda idol on top. However, after this Hindu temple was destroyed by Qutb-ud-din Aybak to build the Qutub Minar and the Quwwat-ul-Islam mosque, it is the only part that remains.

The Delhi Pillar is a curious sight, and despite being exposed to the elements for thousands of years, it shows little sign of rust. Over the decades, scientists and metal engineers from around the world have proposed a number of theories about the nature of this unusual wonder.

Decoding the mystery of the thousand-year-old rust-free iron pillar

It stands 7.2 metres high from the ground and weighs around 10 tonnes. It was moved to its current location hundreds of years ago. It has survived more than 1,600 years of exposure to the elements without rusting. Inscriptions on its body indicate that it was erected to praise the Hindu god and King Chandra – a mysterious king who remains a puzzle to historians.

Legend has it that this iron pillar was cast in memory of King Chamdaro.

But what surprises people is that the iron pillar has been standing exposed for more than 1,600 years, through countless storms and winds, and to this day there is still not a trace of rust.

Iron Pillar of Delhi.

Meanwhile, iron is a metal that rusts very easily after a few decades, let alone over a thousand years.

Until now, people on Earth have not found an effective method to prevent rusting of iron objects. Although pure iron is theoretically rust-free, pure iron is difficult to refine and extremely expensive. Moreover, some scientists have analyzed the composition of iron pillars and discovered that they contain many impurities, not pure iron. And in theory, iron pillars rust more easily than ordinary iron.

If the ancient Indians had mastered the technique of making stainless iron early and it was lost, why didn’t they make other stainless iron products? Moreover, there is not a single record in the ancient Indian book on iron making that mentions this issue.

That iron pillar stands alone, seemingly challenging the intelligence and exploration of mankind, and is also a symbol of ancient Indian civilization.

Obsolete technology creates extraordinary miracles

But finally, experts from the Indian Insтιтute of Technology IIT have solved the mystery of the longevity of the Delhi Iron Pillar . Observing through a microscopic microscope, they discovered an extremely thin “coat” covering the entire surface of this pillar.

Taking samples for research, the composition of the shell was determined to be a compound of iron, oxygen and hydrogen . It was this compound that prevented the iron metal of the pillar from coming into contact with the air. Thanks to that, the corrosion reaction due to the chemical reaction could not occur, making the iron pillar immortal.

Radioisotope analysis also shows that this protective layer began to form about three years after the iron pillar was built, which means that its lifespan is similar to the pillar’s lifespan. Over the millennia, it has been slowly thickening each year. After 1,600 years, the layer is only about 1/20 of a millimeter thick.

The ancient writing is still as sharp as if it had just been engraved, even though thousands of years have pᴀssed.

But how did this iron pillar get such a valuable protective layer? The announcement of a research team has surprised the scientific community around the world: It was the outdated metallurgical technology of the 4th century that accidentally created this compound. Dr. Balasubramanian – the head of the research team said that his team found an unusually high content of phosphorus in the iron sample collected from this pillar.

The phosphorus content analyzed was more than 1%, much higher than the phosphorus content in modern irons today, which is only less than 0.05%. It is this high phosphorus content that acts as a catalyst , promoting the reactions that create the above mentioned protective substance.

This was an accidental achievement, originating from the very primitive metallurgical techniques of that time. Ancient Indians mixed coal with iron ore to shorten the smelting time. With this method, the phosphorus in the iron ore could not be completely separated and remained in the finished iron.

Meanwhile, with modern blast furnace iron smelting technology, phosphorus content can be reduced to very low levels. It is the purity created by modern technology that makes modern iron unable to have the longevity of the Delhi steel pillar.

The discovery of these scientists was further reinforced when people found some weapons such as swords, arrows, knives, etc. in India that were the same age as the Delhi Steel Pillar and they were almost rust-free. This confirmed that it was the primitive metallurgical technique that created surprisingly valuable masterpieces for later generations, making them last forever. The long-standing mystery has been lifted by scientists.