The Red Fort, built by Shah Jahan as a symbol of imperial splendour and since 1947 the ceremonial heart of independent India, is silently darkening. Centuries of history have not scarred it as much as a few decades of modern neglect. Air thick with soot and chemical particles is settling on its sandstone ramparts, creating a thin but insidious black crust. What began as a faint stain is slowly eating into the carvings and arches that have witnessed the nation’s journey from empire to republic.

This is more than a matter of appearance. The fine particulate matter that discolours the walls is also a proven threat to human health. Delhi’s residents breathe the same air that is corroding the fort. The black crust is, quite literally, history’s warning etched in stone. When a monument begins to flake, it tells us that our lungs are already under siege. Protecting the Red Fort and........

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