[blam]

"The pillar—over seven metres high and weighing more than six tonnes—was erected by Kumara Gupta of Gupta dynasty that ruled northern India in AD 320-540. "

540 AD is the date of the cataclismic start of the worldwide Dark Ages. (I wonder if they are related?)

[gcruse]

540 AD is the date of the cataclismic start of the worldwide Dark Ages. (I wonder if they are related?)

Possibly.  Things rust more slowly in the dark, due to slowing interstitial migration of oxygen ions through the iron molecular lattice.  And yes, I am a metallurgist.  I mean, no I'm not.