Standing in the courtyard of the Quwwat-ul-Islam mosque is a 7m-high iron pillar that is of such purity that it hasn’t rusted in over 1600 years. This extraordinary pillar vastly predates the surrounding monuments. A six-line Sanskrit inscription indicates that it was initially erected outside a Vishnu temple, possibly in Bihar, in memory of Chandragupta II, who ruled from AD 375 to 413. What the inscription does not tell is how it was made – scientists have never discovered how the iron could be cast using the technology of the time.
