The Great Hedge of India or Inland Customs Line was a customs barrier across India from the 1840s to the 1880s built by the British rulers to facilitate collecting the heavy salt tax. It was also used to control the profitable opium trade, which the East India Company had acquired from the Mughal Empire by conquest. The barrier consisted of fences, stone walls, and above all a nearly impenetrable barrier of trees, thorny bushes, and hedges, with periodic guard stations.
On the medical effects of salt deprivation, especially if people are working in a hot climate or have dysentery
The links don't cover the economic and quality of life effects of the interruptions to trade and travel caused by the hedge.
Links thanks to james_nicoll.