Rust free Iron Pillar of the 4th century, Delhi - the riddle is not yet fully solved!!

Delhi Iron Pillar.

Qutb Minar and rust free Iron Pillar Delhi.

Weighing 6.3 tons  the 23.08 feet tall  black Iron  Pillar  with a diameter  of  17 inches in the base and 12 inches  at the crest  in the courtyard of Quwwat-ul-Islam Mosque  complex, Delhi  attracts  lots of tourists and also metallurgists /scientists from many parts.  From the look it may pass off as an ordinary pillar of the past era. It it were an ordinary iron pillar, probably long long ago it would have turned into a pile yellow dust.  What is special about this tall  vertically tapering iron pillar?  It was forged in the 4th century with neither  special  protective paint over it nor any cover on it, but  has not rusted  in the last  1700 plus years. The crux of the question is how  come it has withstood continuously the vagaries of weather  for such a long period  with no semblance of rusting so far? The scientists are at their wit's end  and at a loss to come up with a possible explanation regarding its chemical combination that resists rusting and corrosion.

As section of Delhi's Iron Pillar at the

Inscriptions on the iron pillar, Mehrauli,Delhi.

Qutb minar and rust free Iron Pillar

The pillar with roughly 3 feet and 8 inches at the base of the column is below the ground. To give extra  stability to the heavy  iron pillar, the base is set on a grid of a series of iron bars soldered into the upper layer of the stoned pavement. For centuries  studied in depth by the experts in metals, this iron pillar is "a testament to the skill of ancient Indian blacksmiths" of  by-gone era because of its  high resistance to corrosion.  An even layer of crystalline iron hydrogen phosphate forming on the high phosphorus content,  serves to protect it from the effects of the local Delhi climate - extremely hot in the summer and very cold in the winter. Such extreme climatic conditions do impact the stuff made of iron and causes rusting. That it does not promote rusting  over several centuries  is a matter of great surprise and has been an unsolved riddle since 1900s. 

Delhi Iron Pillar.

iron pillar, Mehrauli,Delhi.

The Iron Pillar, in the midst of  Delhi’s most famous monuments, the Qutb Minar, dates back to AD 402 and  since the early part of the 20th century has got the attention of the metallurgists for its rust-proof properties

 There is a  sort of some decorative feature at the top  of the pillar, where a statue of Lord Garuda, or the ‘Sun Bird’, might have been set. According to historians this kind of  feature was  common to many such pillars of the time. The composition of the iron pillar is a subject of  discussion and debate among the scientists. Some postulate  the reason for the continuous resistance  to corrosion  is due to the fact   that the Iron Pillar has a high content of phosphorus and total absence  of Sulphur or magnesium.  This is the reason why the iron  pillar has not rusted even after 1700 years. Yet another positive aspect is this pillar was made to resist  humidity to a greater  extend -  ''about 70 percent, which is appropriate as the climate in Delhi, despite experiencing four seasons in a year, does not ever exceed that limit.” 

The pillar which is made of – 98 percent wrought iron  is listed under the Out-of-Place Artefacts (OOPArts) – a term applied to prehistoric objects from around the world that show technological advancement beyond the time when they were built.  In 2003, experts at the Indian Institute of Technology  came up with an explanation to address the mystery of the pillar’s resistance to rust. They attributed the pillar’s resistance to rust to a thin layer of misawite, a compound of iron, oxygen and hydrogen.

$th century Iron Pillar,

R. Balasubramaniam of the IIT, Kanpur explains how the pillar's resistance to corrosion is due to passive protective film at the iron-rust interface. The presence of second-phase particles (slag and un-reduced iron oxides) in the micro structure of  iron,  high amounts of phosphorus in the metal, and the alternating  wetting and drying  cycles of  atmospheric conditions are the three main factors in the  formation of that protective passive film over the pillar.

 The pillar was installed in its current location by Vigraha Rāja, the ruling Tomar king. The pillar is thought to have originally been erected in what is now Udayagiri by one of the Gupta rulers. The suggested age of 402 CE is  still a matter of serious discussion. This rust free iron pillar at Mehrauli near Qtub complex continues to baffle the scientific community and the common man. 

It was only in the second half of the 19th century the iron pillar drew the attention of the some inquisitive people. One  British soldier  Captain Archer talked about an inscription of unknown antiquity on the pillar, which nobody could read. Later James Prinsep, a British archaeologist studied the inscription in 1838 and translated it into English in the journal of the Asiatic Society of Bengal. According to the inscription a ruler named Chandra,  had conquered the Vangas and Vahlikas. Historians believe reference is made Samudragupta, the real founder of the Gupta Empire in (375–414 AD).

Iron Pillar, Delhi.

 Delhi's  cast Iron Pillar is  a  fine example of massive production of superior quality  iron and it confirms the fact that the Indian steel makers of past era had a good technical know-how and high degree of   accomplishment in the area of hand-forged block of iron. The one at Delhi is the largest forged hand made one, perhaps in the world. 


On the Corrosion Resistance of the Delhi Iron Pillar, R. Balasubramaniam, Corrosion Science, Volume 42 (2000) pp. 2103–2129. "Corrosion Science" is a publication specialized in corrosion science and engineering.