The iron monument is 1,600 years old, but it has never rusted. What explains it?

According to studies of the inscriptions on the metal, the more than six-tonne monument was created during the reign of Chandragupta II, the third ruler of the Gupta Empire, in the fifth century. But even with the capital’s increasing pollution levels and bad weather over the past few years, the 1,600-year-old monument remains relatively untouched.

Scientists have been analyzing the column’s metal since 1912, and between 2000 and 2003 they came to a conclusion about its resistance to corrosion. Second Studies published in Corrosion Science and In current science Created by experts from the Indian Institute of Technology (IIT), the column is made mostly (98%) of wrought iron with high levels of phosphorus, but zero magnesium and sulphur – two elements found in modern iron.

The unique composition is due to the ancient craftsmanship of blacksmithing and welding used in the manufacture of the shaft, heating and hammering the iron, keeping not only the phosphorus intact, but also forming a thin layer of “mesoite” around the structure – a mixture of iron, oxygen and hydrogen (unreduced iron oxides) which, precisely due to exposure to the atmosphere, acts as a protective layer.

The column is described by archaeologist-metallurgist R. Balasubramaniam, author of the study, as “a living testament to ancient Indian metallurgical prowess,” with this very peculiar technique responsible for the material’s resilience. Over the years, other incidents have attested to its durability, such as when a cannonball struck the column in the 18th century but failed to break it, leaving only a “visible dent.”