Iron (Delhi or Qutb) Column

The Iron Pillar in Delhi rises above the central courtyard of the Quwwat-ul-Islam Mosque in the Qutb Minar complex in Mehrauli, Delhi. It is famous for remaining relatively rust-free despite being created over 1600 years ago, around 400 AD. The six-ton pillar was made during the Gupta period, probably in Udayagiri, in the present-day state of Madhya Pradesh. However, there are other versions pointing to Mathura as the original location of the Iron Pillar. At the time of its first erection, the decorative seven-part capital crowning the pillar may have held a figure of Garuda — the bird in Hindu mythology that carries the god Vishnu through the sky.

Some researchers believe that the Iron Pillar was moved from Udayagiri to Delhi by order of Sultan Iltutmish in the 13th century. Others think it was relocated to a temple in Lal Kot, Delhi, by King Tomara Anangapala in 1050 and was moved to its current place near the mosque around 1191. Originally created for a Vishnu temple, the pillar now adorns the grounds of the first mosque on the Indian subcontinent and is considered one of the most important historical monuments in India.

The pillar has a total height of 7.2 meters, including the part buried underground. The cylindrical part above ground measures 5.2 meters from the stone platform, which was probably added in 1871 or 1872. This cylindrical section tapers from a diameter of 42 centimeters at the base (above ground) to 30 centimeters just below the decorative capital. The lower 0.6 meters of the cylindrical part have a rough surface with hammer marks. It is believed that the pillar was originally buried deeper than it is now. One piece of evidence is the rough texture visible at the lower part of the pillar. It has been suggested that this rough texture is not a random defect but was designed to help the pillar hold better in the ground, indicating that this part was originally underground. The base of the pillar appears flat, with eight small projections evenly spaced around the circumference, embedded into a lead plate. The lead plate rests on a dressed stone slab on the original temple floor.

There are Sanskrit inscriptions on the pillar in several places. The oldest is a six-line engraving at a height of 2 meters above the platform. It states that the pillar was created for a Vishnu temple by order of a king named Chandra. This may be King Chandragupta II, but the exact identification is unknown. A later inscription reads, "In Samvat 1109 [1052–53 AD], Ang Pal founded Delhi," indicating the involvement of King Tomara Anangapala.

J. F. Fleet translated the main inscription in 1888 as follows:

“He, on whose arm glory is inscribed with a sword, when in battle in the lands of Vanga (Bengal) he broke (and turned) back the enemies who united against him; – he, through whom, having passed in war through the seven mouths (of rivers) of the Sindhu, the Vahlikas were subdued; – he, by whose breath the southern ocean still smells sweet.

He, the remnant of great zeal, whose energy, having destroyed (his) enemies, like (the remnant of a great blazing heat) of a dying fire in a great forest, still does not leave the land; although he, the king, weary, left this land and went to the other world, having transmigrated (bodily) from the land (of paradise) conquered (by his merits), (yet) remaining on (this) land (as the memory of his) glory.

By him, the king who attained sole supreme sovereignty in the world, acquired by his own hand and (enjoyed) for a very long time, (and) bearing the name Chandra, with a face as beautiful as the full moon, – with faith directed to (the god) Vishnu, this exalted standard of divine Vishnu was set up on the hill (called) Vishnupada.”

The pillar was erected in 415 AD in honor of King Chandragupta II, who died in 413 AD. Originally, it was located in the western part of the country in a Vishnu temple complex in the city of Mathura. The pillar was topped with an image of the sacred bird Garuda and stood in front of the temple. In 1050, King Anangapala moved it to Delhi. According to other sources, the temple complex was destroyed in the 13th century by order of the first Delhi Sultan; at that time, the pillar was moved to Delhi.

The pillar is mentioned by Al-Biruni of Khwarezm in 1048:

“The Arabs found an iron pillar 70 cubits high. Hisham ibn Amir ordered it to be dug up to the base, and it was discovered that the pillar was buried another 30 cubits into the ground. Then he inquired about it and was told that a Tubba from Yemen entered their country along with the Persians, and when they conquered India, the Yemenis forged this pillar from their swords and said: ‘We do not want to go further from here to another country,’ and took possession of Sindh.”

The presence of such a large iron artifact in the 5th century symbolized the high level of wealth of the state. Even 600 years later, describing the pillar (from others’ words), Al-Biruni considered it merely a legend.

Jawaharlal Nehru wrote in his book “The Discovery of India”:

Ancient India evidently achieved great success in ironworking. Near Delhi stands a huge iron pillar that baffles modern scientists who cannot determine the method of its manufacture that protected the iron from oxidation and other atmospheric effects.

The Iron Pillar in Delhi gained popularity among Europeans after the works of the English orientalist and Indologist Alexander Cunningham. The information he provided about 150 years ago is now criticized by researchers. Cunningham claimed the pillar’s height was at least 18 meters and its weight 17 tons. Moreover, from his description, the pillar appeared to be solid, not welded. These assumptions were adopted by historians, and even later scientific studies could not shake their belief in the miraculous properties of the “eternal” pillar.

A similar pillar, almost twice as tall, made in the 3rd century and now preserved only in fragments, was installed in the Indian city of Dha.

The pillar has been studied by many metallurgists, with the initial analysis completed in 1912. The artifact was thoroughly researched by metallurgist Ramamurti Balasubramaniam (1961–2009), professor of materials science and metallurgical engineering at the Indian Institute of Technology Kanpur. In 2005, he published the book "The History of the Iron Pillar of Delhi," which explores the history, manufacture, and composition of the pillar. The artifact consists mainly of iron with small impurities of phosphorus (0.25 percent), carbon (0.15 percent), manganese (0.05 percent), nickel (0.05 percent), silicon (0.05 percent), copper (0.03 percent), nitrogen (0.02 percent), and sulfur (0.005 percent). The pillar was likely created in a horizontal position using forge welding techniques. This method involved using intense heat to join pieces of iron weighing 40–50 pounds (18–23 kilograms) each. The capital was made from seven separate parts, which were mounted on a hollow cylinder and then inserted into the body of the pillar.

Most likely, the pillar was made by forging individual blooms of iron weighing up to 36 kg. Evidence includes clearly visible hammer marks and forge welding lines, as well as the low sulfur content (due to charcoal used for smelting the ore) and a large amount of non-metallic inclusions, i.e., slag, remaining from poor forging of individual sections.

Guides often tell tourists that stainless steel was used to create this monument. However, analysis by Indian scientist Chedari shows that the Delhi pillar does not contain significant amounts of alloying elements that increase corrosion resistance, whereas all stainless steels are alloyed.

Opposite opinions held that the pillar was made of very pure iron (there are even claims of “chemically pure,” “atomic,” and similar). This hypothesis appeared for years in metallurgy textbooks as an example of high atmospheric resistance of pure iron. In reality, the pillar’s material impurity content (0.278%) does not even reach technically pure iron, which contains no more than 0.14% impurities. The most accurate name for the pillar’s material is wrought, forge-welded, or bloomery iron.

There is nothing fantastic about producing iron with such impurity content in ancient times; it is enough to start with quality raw materials (ore, charcoal) and carefully forge the billet to remove most of the slag. Iron was produced in this way throughout the pre-industrial era until the advent of puddling. The real challenge for ancient metallurgists was producing iron with a specified carbon content, i.e., steel — until the invention of the Bessemer converter, all methods of steel production (carburization, bloomery refining) were inefficient and unstable.

Products made from forge-welded and puddled iron indeed have higher atmospheric resistance compared to modern steels, especially high-grade ones. Ships, bridge trusses, firearm parts, and other items made from this material rarely required special corrosion protection — the naturally forming surface oxide film successfully performed this function. Corrosion protection methods began to be developed only after the late 19th century transition to industrial production of more corrosion-prone carbon steels smelted on coal and containing more sulfur than ancient steels smelted on charcoal.

A popular hypothesis was that the Delhi pillar was made from meteoritic iron. It is known to resist corrosion well. But meteoritic iron always contains nickel, and nickel was not found in the iron of the Indian pillars.

The Iron Pillar in Delhi has also attracted the attention of ufologists, who link its origin to extraterrestrial civilizations.

The main reason for the Delhi pillar’s resistance to atmospheric corrosion is the phenomenon of metal passivation — a naturally formed oxide film on its surface prevents further corrosion. Secondary reasons include the increased phosphorus content in the pillar’s metal, which, although not an anticorrosion additive by itself, enhances the steel surface’s ability to passivate, and the low humidity of Delhi’s air. The pillar is much less resistant to electrochemical corrosion — its buried part has suffered significant corrosion. A similar pillar from Konark, located near the sea, is heavily corroded.

The pillar is embedded in the ground, and this part is covered with a centimeter-thick layer of rust, pitted in places with deep cavities.

Several hypotheses explain the anticorrosion resistance of the above-ground part of the iron pillar by the dryness of Delhi’s atmospheric air.

Swedish metallurgist Wranglen conducted experiments where pieces cut from the pillar were taken to the seacoast and industrial areas of Sweden (marine and industrial atmospheres are most dangerous for steel), where they corroded successfully. The underground part of the pillar, studied by the same J. Wranglen, is covered with a rust layer one centimeter thick. Corrosion pits up to 10 centimeters deep have also been found.

In 1953, Hudson published in the journal “Nature” a report on the corrosion rates of copper steel and zinc in various climates, including near the pillar. Delhi’s atmosphere ranked second to last in aggressiveness, surpassed only by the atmosphere in Khartoum, which is even drier. Even during monsoon periods, Delhi’s air humidity exceeded the critical value (70%) at which steel noticeably corrodes only in the morning hours. Even unstable zinc oxidizes very little in Delhi’s atmosphere.

Indian scientist Balasubramaniam analyzed the composition and anticorrosion properties of the pillar, and in 2000 his work was published, providing detailed tables of the chemical composition of the above-ground and underground parts of the pillar. It consists of iron, lacking manganese and almost nickel-free.

Although many consider the lack of rust on the pillar a mystery, scientists have several theories attempting to explain this phenomenon. These theories can be divided into two main categories. The first is a climatic explanation: the relative humidity in Delhi is below 70 percent for most of the year, corresponding to a low level of rust. However, the meteorological data on which this information is based were collected over a short period (from 1930 to 1960), which is insufficient to determine the climatic conditions over the entire existence of the pillar. Moreover, the climate of the pillar’s original location should be considered. After nearly a decade of self-funded research, Balasubramaniam proposed a second theory based on chemistry. As the pillar ages and rusts, chemical changes occur involving phosphates, which create a thin protective layer of hydrated iron phosphate covering the pillar’s surface. Phosphorus in the iron allows these reactions to occur. The ancient Indians were excellent blacksmiths, and Balasubramaniam argued that the pillar’s creators understood the connection between phosphorus content and limited rusting. He believed they deliberately chose iron ore with a high phosphorus content.

As a result of thorough research, it was established that the thickness of the oxide layer on the Delhi pillar corresponds to the steel corrosion rate in this city.

Additionally, since the pillar has long been (and remains) an object of cult reverence and later a special landmark, it has never been left unattended by people.

Religious rituals required anointing the pillar with oils and incense. Thanks to this, the pillar constantly had a film protecting it from corrosion.

Balasubramaniam, comparing ancient iron production technologies with modern ones and analyzing archaeological finds, noted that in ancient times phosphorus was not effectively removed (through slags) and remained in the metal. Later steel production technologies could not allow high phosphorus content because steel became brittle. Later technologies used lime, which also removed phosphorus into slag, which was absent in old technologies (as shown by the absence of lime and phosphorus in old slags). The presence of phosphorus is the reason for corrosion resistance.

There is a version that when smelting “by eye,” as was done in ancient times, very large deviations in metal quality were possible. The pillar could be one such exception. Modern atmospheric steels (for example, steel 10KhNDP) have their features due to high phosphorus content. When copper and phosphorus, as well as chromium, interact with oxygen, carbon dioxide, and water vapor, they form sparingly soluble compounds that are part of the oxide film enveloping the steel. This film protects the metal well. The corrosion rate of structures under such protection under normal conditions is about 0.3 mm per 100 years.

Such steels under the brand “Corten” were invented in the USA in the 1930s and contained up to 0.15% phosphorus. The Delhi pillar contains 0.11–0.18% phosphorus.

Sources:

https://www.britannica.com/topic/Iron-Pillar-of-Delhi

Mezenin, N. A. The Iron Pillar in Delhi: [arch. December 23, 2010] // Fascinating about Iron. — Moscow: Metallurgy, 1972. — pp. 52–53. — 200 pages.

https://ru.wikipedia.org/wiki/Железная_колонна_в_Дели