Experts at the Indian Institute of Technology have resolved the mystery behind the 16,00-year-old iron pillar in Delhi, which has never corroded despite the Capital's harsh weather. Metallurgists at IIT Kanpur have discovered that a thin layer of misawite, a compound of iron, oxygen and hydrogen, has protected the cast iron pillar from rust. The protective film formed within three years of the pillar's installation and has been growing ever so slowly since then. After 1,600 years, the film has grown just one-twentieth of a millimeter thick, according to R Balasubramanium of the IIT.