An iron seven-meter column, part of the architectural ensemble of Qutub Minar. This is one of the main attractions of Delhi. Its uniqueness lies in the fact that over the centuries it has hardly undergone corrosion. It has been suggested that the reason for this is a special metal and a favorable climate. According to another version, the column was preserved because of the oils that the pilgrims rubbed it with. But none of the hypotheses has been officially confirmed: it is still unclear how the prototype of modern weather-resistant steel was obtained in 415.