Qutub Minar’s iconic 1600-year-old iron pillar is still completely rust-free. IITians decode the ancient science behind it’s evergreen surface

One iron pillar stands strong and proud, with not even a hint of rust, for the past 1600 centuries. Located at New Delhi’s UNESCO-listed Qutb Minar complex, the 7.2 metre tall pillar looks as new and robust (and rust free!) as ever. Under normal conditions, structures made from iron or iron-based alloys gradually react with moisture and oxygen in the environment. This chemical process, known as oxidation, causes the metal surface to corrode and develop a layer of reddish-brown rust over time. Unless preventive measures are taken, prolonged exposure to rain, humidity, or damp conditions can weaken the material and accelerate deterioration.

How Did The Structure Defy Erosion?

According to a CNN report, in 2003, a group of researchers from IIT Kanpur decoded the secret behind the iron pillar being rust free. Hey discovered that the pillar, made from wrought iron, has high phosphorus content and lacks sulphur and magnesium unlike modern iron. Moreover artisans used a technique called forge welding which helped the iron brave against rust. They heated and hammered the iron, maintaining the phosphorus content at high levels.

Additionally, a layer of misawite - a compound of iron, oxygen and hydrogen was found on the pillar’s surface. This layer is formed in presence of high phosphorus and absence of lime. This has helped helped pillar brave the vagaries of weather.


"In summary, the microstructural and compositional inhomogeneities of the Delhi pillar iron do not have any influence on the protective passive film that forms on the surface. The deciding factor this is imparting the excellent corrosion resistance is the high phosphorus content of the Delhi pillar iron," the study reported.

The Iron Pillar was incorporated into the Quwwat-ul-Islam Mosque and the larger Qutb Complex during the thirteenth century under the rule of Shams ud-Din Iltutmish. Historians believe it was erected within the complex as a symbol of prestige and conquest. However, scholars continue to debate the pillar's original location before it became part of the monument.

As per an inscription of king Chandra, the pillar was erected at Vishnupadagiri. Scholar J.F Fleet identified the place as Mathura because of its nearness to Delhi and the city's reputation as a pilgrimage centre. Other scholars Meera Dass and R Balasubramanian theorised that the pillar was originally established in the Udayagiri caves. The theory was based on the fact that the inscription mentions the place Vishnupada-giri.

The exact circumstances surrounding the Iron Pillar's relocation to Delhi remain uncertain, and there's no unanimous theory as to when this incident couls have taken place. One prominent theory was proposed by Alexander Cunningham, who suggested that the pillar was brought to Delhi by Anangpal Tomar, a ruler of the Tomara dynasty.

In 2009, Finbarr Barry Flood theorised that Iltutmish, the third Sultan of Delhi may have had moved the pillar to Delhi. According to this theory, the pillar was originally erected at Vidisha, and was moved by Iltutmish to the Qutb complex when he destroyed Vidisha in the thirteenth century.