Qutab Minar is the actual site of Hindu Temples of Lal Kot

Inspired by the Minaret of Jam in Afghanistan and wishing to surpass it, Qutb-ud-din Aibak, the first Muslim ruler of Delhi, commenced construction of the Qutb Minar in 1193, but could only complete its base. His successor, Iltutmish, added three more stories and, in 1386, Firuz Shah Tughluq constructed the fifth and the last story. The development of architectural styles from Aibak to Tughluq are quite evident in the minaret. Like earlier towers erected by the Ghaznavids and Ghurids in Afghanistan, the Qutb Minar comprises several superposed flanged and cylindrical shafts, separated by balconies carried on Muqarnas corbels. The minaret is made of fluted red sandstone covered with intricate carvings and verses from the Qur'an. The Qutb Minar is itself built on the ruins of the Lal Kot, the Red Citadel in the city of Dhillika, the capital of the Tomars and the Chauhans, the last Hindu rulers of Delhi. The complex initially housed 27 ancient Jain temples which were destroyed and their debris used to build the Qutb minar. One engraving on the Qutb Minar reads, "Shri Vishwakarma prasade rachita" (Conceived with the grace of Vishwakarma), this is thought to have been engraved by the ancient Hindu craftsmen who built the Lal Kot and its Hindu Temples!

The Tomar Rajput dynasty founded Lal Kot in 736 near the Qutub Minar, at Mehrauli. The Prithviraj Raso names the Rajput Anangpal as the founder of Lal Kot.

An contemporary account of the city of Delhi in the Tomar period is given by Vibudh Shridhar. He describes an immense fort surrounded by a moat besides the Ananga lake. The markets were full of commodities like cloth, grain, betel-nuts, sweets etc as well as accounting books. He also implies that Delhi was a center of learning where eloquent language was spoken. The pinnacles of the city gates were guilded with gold and buildings were studded with gems.

The Chauhan Rajput kings of Ajmer conquered Lal Kot in 1180 and renamed it Qila Rai Pithora. The Chauhan king Prithviraj III was defeated in 1192 by the Afghan Muhammad Ghori. Anangpal Tomar, a Chandravanshi Rajput ruler of Delhi , often described as the founder of Delhi, built the citadel some 10 kilometres from Suraj Kund around 731. Dhilli' was founded by Tomar Anangapala according to Vibudh Shridhar and other later authors. Lal Kot built by the Tomar was renamed Qila Rai Pithora after Prithvi Raj Chauhan. It was a seven-gated fort in Delhi. Prithviraj, a Chauhan king was the second last Hindu king of Delhi.

The nearby Iron Pillar is one of the world's foremost metallurgical curiosities, standing in the famous Qutb complex. According to the traditional belief, anyone who can encircle the entire column with their arms, with their back towards the pillar, can have their wish granted. Because of the corrosive qualities of sweat the government has built a fence around it for safety.

It was then closed a few years later-due to a stampede which killed many people. The iron pillar of Delhi, India is a 7 meter (22 feet) high pillar in the Qutb complex which is a curiosity because of the composition of the metals used in its construction.

The pillar—almost seven meters (22 feet) high and weighing more than six tons—was allegedly fashioned at the time of Chandragupta II Vikramaditya (375–413), though other authorities give dates as early as 912 BCE. The pillar initially stood in the centre of a Hindu Temple complex housing twenty-seven temples that were destroyed by Qutb-ud-din Aybak, and their material was used in building the Qutub Minar and Quwwat-ul-Islam mosque. The pillar and ruins of the temple stand all around the Qutb complex today. The pillar is 98% wrought iron of pure quality, and is a testament to the high level of skill achieved by ancient Indian ironsmiths. It has attracted the attention of both archaeologists and metallurgists, as it has withstood corrosion for over 1600 years in the open air.

The name Delhi may be derived from the word 'Dhillika', though there are other theories. According to Satyarth Prakash (1875 CE) of Swami Dayanand, Raja Dhilu (King Dihlu) founded ancient Delhi in 800 BC. It was the name of the first medieval township of Delhi, located on the southwestern border of the present Delhi, in Mehrauli. This was the first in the series of seven medieval cities. It is also known as Yoginipura, that is, the fortress of the yoginis (female divinities). It gained importance during the time of Ananga Pala Tomar. In the 12th century, the city was included in the dominions of Prithviraj Chauhan.

Pasanaha Chariu of Vibudh Shridhar (VS 1189-1230) an Apabhramsha writer, provides the first referenece to the legend of the origin of the name Dhilli for Delhi.

हरियाणए देसे असंखगाम, गामियण जणि अणवरथ काम|
परचक्क विहट्टणु सिरिसंघट्टणु, जो सुरव इणा परिगणियं|
रिउ रुहिरावट्टणु बिउलु पवट्टणु, ढिल्ली नामेण जि भणियं|

Translation: There are countless villages in Haryana country. The villagers there work hard. They don't accept domination of others, and are experts in making the blood of their enemies flow. Indra himself praises this country. The capital of this country is Dhilli.

जहिं असिवर तोडिय रिउ कवालु, णरणाहु पसिद्धउ अणंगवालु ||
वलभर कम्पाविउ णायरायु, माणिणियण मणसंजनीय ||

Translation: The ruler Anangapal is famous, he can slay his enemies with his sword. The weight (of the Iron pillar) caused the Nagaraj to shake.

A VS 1383 inscription in Delhi Museum confirms the founding of Delhi by the Tomars:

देशोऽस्ति हरियानाख्यो पॄथिव्यां स्वर्गसन्निभः |
ढिल्लिकाख्या पुरी तत्र तोमरैरस्ति निर्मिता ||

Prithviraj Raso also confirms the founding by the Tomars and the legend of the loose nail:

हुं गड्डि गयौ किल्ली सज्जीव हल्लाय करी ढिल्ली सईव |
फिरि व्यास कहै सुनि अनंगराइ भवितव्य बात मेटी न जाइ ||

Description

The pillar, almost seven meters high and weighing more than six tons, was erected by Chandragupta II Vikramaditya (375 CE–414 CE), (interpretation based on analysis of archer type Gupta gold coins) of the Gupta dynasty that ruled northern India 320–540. The pillar with the statue of Chakra at the top was originally located at a place called Vishnupadagiri (meaning “hill with footprint of Lord Vishnu”). This has been identified as modern Udayagiri, situated in the vicinity of Besnagar, Vidisha and Sanchi. These towns are located about 50 kilometres east of Bhopal, in central India. There are several aspects to the original site of the pillar at Udayagiri. Vishnupadagiri is located on the Tropic of Cancer and, therefore, was a centre of astronomical studies during the Gupta period. The Iron Pillar served as a sundial when it was originally at Vishnupadagiri. The early morning shadow of the Iron Pillar fell in the direction of the foot of Anantasayin Vishnu (in one of the panels at Udayagiri) only around the summer solstice (June 21). The Udayagiri site in general, and the Iron Pillar location in particular, are evidence for the astronomical knowledge that existed in Gupta India.

The pillar bears a Sanskrit inscription in Brahmi script which states that it was erected as a standard in honour of Lord Vishnu. It also praises the valor and qualities of a king referred to simply as Chandra, who has been identified with the Gupta King Chandragupta II Vikramaditya (375-413). The inscription reads (in the translation given in the tablets erected by Pandit Banke Rai in 1903):

He, on whose arm fame was inscribed by the sword, when, in battle in the Vanga countries (Bângal), he kneaded (and turned) back with (his) breast the enemies who, uniting together, came against (him);-he, by whom, having crossed in warfare the seven mouths of the (river) Sindhu, the Vâhlikas were conquered;-he, by the breezes of whose prowess the southern ocean is even still perfumed;- (Line 3.)-He, the remnant of the great zeal of whose energy, which utterly destroyed (his) enemies, like (the remnant of the great glowing heat) of a burned-out fire in a great forest, even now leaves not the earth; though he, the king, as if wearied, has quit this earth, and has gone to the other world, moving in (bodily) from to the land (of paradise) won by (the merit of his) actions, (but) remaining on (this) earth by (the memory of his) fame;- (L. 5.)-By him, the king,-who attained sole supreme sovereignty in the world, acquired by his own arm and (enjoyed) for a very long time; (and) who, having the name of Chandra, carried a beauty of countenance like (the beauty of) the full-moon,-having in faith fixed his mind upon (the god) Vishnu, this lofty standard of the divine Vishnu was set up on the hill (called) Vishnupada.

It is believed by some that the pillar was installed in its current location by Vigraha Raja, the ruling Rajput Tomar king. One of the inscriptions on the iron pillar from A.D. 1052 mentions Rajput king Anangpal II.

Made up of 98% wrought iron of pure quality, it is 7.21m (23 feet 8 inches) high, with 93 cm buried below the present floor level, and has a diameter of 41 cm (16 inches) at the bottom which tapers towards the upper end. The pillar was manufactured by forge welding. The temperatures required to form such a pillar by forge welding could only have been achieved by the combustion of coal. The pillar is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron.

A fence was erected around the pillar in 1997 because visitors were damaging the pillar. There is a popular tradition that it was considered good luck if you could stand with your back to the pillar and make your hands meet behind it.

Scientific analysis

In a report published in the journal Current Science, R. Balasubramaniam of the IIT Kanpur explains how the pillar's resistance to corrosion is due to a passive protective film at the iron-rust interface. The presence of second phase particles (slag and unreduced iron oxides) in the microstructure of the iron, that of high amounts of phosphorus in the metal, and the alternate wetting and drying existing under atmospheric conditions, are the three main factors in the three-stages formation of that protective passive film.

Lepidocrocite and goethite are the first amorphous iron oxyhydroxides that appear upon oxidation of iron. High corrosion rates are initially observed. Then an essential chemical reaction intervenes: slag and unreduced iron oxides (second phase particles) in the iron microstructure alter the polarization characteristics and enrich the metal–scale interface with P, thus indirectly promoting passivation of the iron (cessation of rusting activity). The second phase particles act as a cathode, and the metal itself serves as anode, for a mini-galvanic corrosion reaction during environment exposure. Part of the initial iron oxyhydroxides is also transformed into magnetite, which somewhat slows down the process of corrosion. But the ongoing reduction of lepidocrocite, and the diffusion of oxygen and complementary corrosion through the cracks and pores in the rust, still contribute to the corrosion mechanism from atmospheric conditions.

The next main agent to intervene in protection from oxidation is phosphorus, enhanced at the metal–scale interface by the same chemical interaction previously described between the slags and the metal. The ancient Indian smiths did not add lime to their furnaces. The use of limestone as in modern blast furnaces yields pig iron that is later converted into steel; in the process most phosphorus is carried away by the slag. The absence of lime in the slag, and the deliberate use of specific quantities of wood with high phosphorus content (for example Cassia auriculata) during the smelting, induces a higher P content (> 0.1%, average 0.25%) than in modern iron produced in blast furnaces (usually less than 0.05 per cent). There is also more phosphorus as solid solution throughout the metal than in the slags (one analysis gives 0.10% in the slags for 18% in the iron itself, for a total P content of 0.28% in the metal). This high P content and particular repartition are essential catalysts in the formation of a passive protective film of “misawite” (d-FeOOH), an amorphous iron oxyhydroxide that forms a barrier by adhering next to the interface between metal and rust. Misawite, the initial corrosion-resistance agent, was thus named because of the pioneering studies of Misawa and co-workers on the effects of P and Cu and those of alternating atmospheric conditions, in rust formation.

The most critical corrosion-resistance agent is iron hydrogen phosphate hydrate (FePO₄-H₃PO₄-4H₂O) under its crystalline form and building up as a thin layer next to the interface between metal and rust. Rust initially contains iron oxide/oxyhydroxides in their amorphous forms. Due to the initial corrosion of metal, there is more P at the metal–scale interface than in the bulk of the metal. Alternate environmental wetting and drying cycles provide the moisture for phosphoric acid formation. Over time the amorphous phosphate is precipitated into its crystalline form (the latter being therefore an indicator of old age, as this precipitation is a rather slow happening). The crystalline phosphate eventually forms a continuous layer next to the metal, which results in an excellent corrosion resistance layer. In 1,600 years the film has grown just one-twentieth of a millimetre thick.

Balasubramaniam states that the pillar is "a living testimony to the skill of metallurgists of ancient India". An interview with Balasubramaniam and his work can be seen in the recent article by Veazy.

It was claimed in the 1920s that iron manufactured in Mirjati near Jamshedpur is similar to the iron of the Delhi pillar. Further work on Adivasi (tribal) iron by the National Metallurgical Laboratory in the 1960s did not verify this claim.

According to INTACH, further research has been proposed on the Iron Pillar to study the ancient metallurgy of India. The ASI is reported to have has concurred for the proposed studies that would make comparisons by testing other ancient iron objects like the pillar at Dhar, the iron beams at Konarak, and so forth. The present research using non– intrusive technique as proposed by Dr.Baldev Raj who is the Director of the Indira Gandhi Centre for Atomic Research and a member of the panel of architects and scientists.