Qutb Minar - Greensward
This iron pillar -- which is 7.3 meters tall -- dates from the period 375-414 or even as early as 912 BCE. The intriguing aspect of the pillar is that it has not rusted in about 2000 years. It is known to be 98% iron, 0.25% P, 0.15% C, with much smaller amounts of S, Si, N, Mn, Cu, and Ni. It is apparently the high phosphorus content that has kept the pillar from rusting. 
See http://en.wikipedia.org/wiki/Iron_pillar_of_Delhi. Also see refs. therein.

This iron pillar -- which is 7.3 meters tall -- dates from the period 375-414 or even as early as 912 BCE. The intriguing aspect of the pillar is that it has not rusted in about 2000 years. It is known to be 98% iron, 0.25% P, 0.15% C, with much smaller amounts of S, Si, N, Mn, Cu, and Ni. It is apparently the high phosphorus content that has kept the pillar from rusting.
See http://en.wikipedia.org/wiki/Iron_pillar_of_Delhi. Also see refs. therein.