India, Aug. 26 -- Everyday life in 19th-century India involved a barrier larger than most European borders. It was built for the single purpose of keeping salt out of dinner pots.

Salt, under the British Raj, became one of the state's most heavily taxed commodities. To protect this revenue, colonial administrators created a 4,000-kilometre wall of thorns across the country.

'The Great Hedge of India' was a vast network of thorny bushes, trees, brushwood, customs posts and patrol routes designed to stop untaxed salt from entering areas where the British charged higher duties.

Everyone needed salt and the colonisers knew to capitalise on it. Thus began the story of the hedge.

The problem was caused by different salt prices and taxes acr...