The iron pillar (also known as the Ashokan pillar) of Delhi, India, is a 7 m (23 ft) high pillar in the Qutb complex, notable for the composition of the metals used in its construction.
The pillar, which weighs more than six tons, is said to have been fashioned at the time of Chandragupta Vikramaditya (375–413) of the Gupta Empire,[1] though other authorities give dates as early as 912 BCE.[2] The pillar initially stood in the center of a Jain temple complex housing twenty-seven temples that were destroyed by Qutb-ud-din Aybak, and their material was used in building the Quwwat-ul-Islam mosque and the Qutub Minar complex where the pillar stands today.[3]
The pillar has attracted the attention of archaeologists and metallurgists and has been called "a testament to the skill of ancient Indian blacksmiths" because of its high resistance to corrosion.[4] The corrosion resistance results from an even layer of crystalline iron hydrogen phosphate forming on the high phosphorus content iron, which serves to protect it, and also the effects of the local Delhi climate, which alternates from wet to dry. [5]
The name of the city of Delhi is thought to be based on a legend associated with the pillar (see History of Delhi).