Iron pillar @ Delhi

Standing at the center of the Quwwatul Mosque the Iron Pillar is one of Delhi's most curious structures. Dating back to 4th century A.D., the pillar bears an inscription which states that it was erected as a flagstaff in honour of the Hindu god, Vishnu, and in the memory of the Gupta King Chandragupta II (375-413). How the pillar moved to its present location remains a mystery. The pillar also highlights ancient India's achievements in metallurgy. The pillar is made of 98 per cent wrought iron and has stood 1,600 years without rusting or decomposing.

7.3 m tall, with one meter below the ground; the diameter is 48 centimeters at the foot, tapering to 29 cm at the top, just below the base of the wonderfully crafted capital; it weighs approximately 6.5 tones, and was manufactured by forged welding..

Corrosion, of a different kind:

I was very taken up with a saying of the Buddha, cited from the Dhammapada, which serves as an epigraph at the beginning of the book. This is how it runs:
"As rust, sprung from iron, eats itself away when arisen, even so his own deeds lead the transgressor to states of woe…."

Mystery of Delhi's Iron Pillar unraveled :

Experts at the Indian Institute of Technology have resolved the mystery behind the 1,600-year-old iron pillar in Delhi, which has never corroded despite the capital's harsh weather.

The protective film took form within three years after erection of the pillar and has been growing ever so slowly since then. After 1,600 years, the film has grown just one-twentieth of a millimeter thick.