Visitors to the courtyard of the complex’s Quwwat-ul-Islam Mosque will immediately spot an imposing 7.2-meter, six-ton iron pillar with a decorative top that’s even older than the complex.

An iron pillar placed in the UNESCO-listed Qutub Minar complex in New Delhi has long fascinated scientists for surviving over 1,600 years without rust. Standing tall at 7.2 metres and weighing six ...