The iron pillar is one of the world’s foremost metallurgical curiosities. The pillar, almost seven meters high and weighing more than six tonnes, was erected by Chandragupta II Vikramaditya (375–414 CE), (interpretation based on careful analysis of archer type Gupta gold coins) of the Gupta dynasty that ruled northern India 320–540.
It is famous for the rust-resistant composition of the metals used in its construction. The pillar weighs over six tonnes (13,228 lb) and is thought to have been erected elsewhere, perhaps outside the Udayagiri Caves, and moved to its present location early in the Delhi Sultanate.
While the pillar was certainly used as a trophy in building the Quwwat-ul-Islam mosque and the Qutb complex, its original location, whether on the site itself or from elsewhere, is debated.
According to the inscription of king Chandra, the pillar was erected at Vishnupadagiri (Vishnupada). J. F. Fleet (1898) identified this place with Mathura, because of its proximity to Delhi (the findspot of the inscription) and the city's reputation as a Vaishnavite pilgrimage center. However, archaeological evidence indicates that during the Gupta period, Mathura was a major center of Buddhism, although Vaishnavism may have existed there. Moreover, Mathura lies in plains, and only contains some small hillocks and mounds: there is no true Giri (hill) in Mathura.
Based on paleographic similarity to the dated inscriptions from Udayagiri, the Gupta-era iconography, analysis of metallurgy, and other evidence, Meera Dass and R. Balasubramaniam (2004) theorized that the iron pillar was originally erected at Udayagiri.
According to them, the pillar, with a wheel or discus at the top, was originally located at the Udayagiri Caves. This conclusion was partly based on the fact that the inscription mentions Vishnupada-giri.
This conclusion was endorsed and elaborated by Michael Willis in his Archaeology of Hindu Ritual, published in 2009. The key point in favor of placing the iron pillar at Udayagiri is that this site was closely associated with Chandragupta and the worship of Vishnu in the Gupta period. Also, there are well-established traditions of mining and working iron in central India, documented particularly by the iron pillar at Dhar and local places names like Lohapura and Lohangī Pīr (see Vidisha). The king of Delhi, Iltutmish, is known to have attacked and sacked Vidisha in the thirteenth century and this would have allowed him to remove the pillar as a trophy to Delhi, just as the Tughluq rulers brought Asokan pillars to Delhi in the 1300s.
It is not certain when the pillar was moved to Delhi from its original location. Alexander Cunningham attributed the relocation to the Tomara king Anangpal, based on the short pillar inscription ascribed to this king. Pasanaha Chariu, an 1132 CE Jain Apabhramsha text composed by Vibudh Shridhar, states that "the weight of his pillar caused the Lord of the Snakes to tremble". The identification of this pillar with the iron pillar lends support to the theory that the pillar was already in Delhi during Anangpal's reign.
Another theory is that the relocation happened during the Muslim rule in Delhi. Some scholars have assumed that it happened around 1200 CE when Qutb al-Din Aibak commenced the construction of the Qutb complex as a general of Muhammad of Ghor. Finbarr Barry Flood (2009) theorizes that it was Qutb al-Din's successor Iltutmish (r. 1210–1236 CE), who moved the pillar to Delhi.