The Inland Customs Line, incorporating the Great Hedge of India (or Indian Salt Hedge), was a customs barrier built by the British colonial rulers of India to prevent smuggling of salt from coastal regions in order to avoid the substantial salt tax.

The customs line was begun under the East India Company and continued into direct British rule. The line had its beginnings in a series of customs houses established in Bengal in 1803 to prevent the smuggling of salt to avoid the tax. These customs houses were eventually formed into a continuous barrier that was brought under the control of the Inland Customs Department in 1843.

The line was gradually expanded as more territory was brought under British control until it covered more than 2,500 miles (4,000 km), often running alongside rivers and other natural barriers. It ran from the Punjab in the northwest to the princely states of Orissa, near the Bay of Bengal, in the southeast. The line was initially made of dead, thorny material such as the Indian plum but eventually evolved into a living hedge that grew up to 12 feet (3.7 m) high and was compared to the Great Wall of China. The Inland Customs Department employed customs officers, jemadars and men to patrol the line and apprehend smugglers, reaching a peak of more than 14,000 staff in 1872.

The line and hedge were abandoned in 1879 when the British seized control of the Sambhar Salt Lake in Rajasthan and applied tax at the point of manufacture. The salt tax itself remained in place until 1946.

When the Inland Customs Line was first conceived, British India was governed by the East India Company. This situation lasted until 1858 when the responsibility for government of the colony was transferred to the Crown following the events of the Indian Rebellion of 1857. By 1780 Warren Hastings, the company's Governor-General of India, had brought all salt manufacture in the Bengal Presidency under company control. This allowed him to increase the ancient salt tax in Bengal from 0.3 rupees per maund (37 kg) to 3.25 rupees per maund by 1788, a rate that it remained at until 1879. This brought in 6,257,470 rupees for the 1784–85 financial year, at a cost to an average Indian family of around two rupees per year (two months' income for a labourer). There were taxes on salt in the other British India territories but the tax in Bengal was the highest, with the other taxes at less than a third of the Bengal tax rate.

It was possible to avoid paying the salt tax by extracting salt illegally in salt pans, stealing it from warehouses or smuggling salt from the princely states which remained outside of direct British rule. The latter was the greatest threat to the company's salt revenues. Much of the smuggled salt came into Bengal from the west and the company decided to act to prevent this trade. In 1803 a series of customs houses and barriers were constructed across major roads and rivers in Bengal to collect the tax on traded salt as well as duties on tobacco and other imports. These customs houses were backed up by "preventative customs houses" located near salt works and the coast in Bengal to collect the tax at source.

These customs houses alone did little to prevent the mass avoidance of the salt tax. This was due to the lack of a continuous barrier, corruption within the customs staff and the westward expansion of Bengal towards salt-rich states. In 1823 the Commissioner of Customs for Agra, George Saunders, installed a line of customs posts along the Ganges and Yamuna rivers from Mirzapur to Allahabad that would eventually evolve into the Inland Customs Line. The main aim was to prevent salt from being smuggled from the south and west but there was also a secondary line running from Allahabad to Nepal to prevent smuggling from the Northwest frontier. The annexation of Sindh and the Punjab allowed the line to be extended north-west by G. H. Smith, who had become Commissioner of Customs in 1834. Smith exempted items such as tobacco and iron from taxation to concentrate on salt and was responsible for expanding and improving the line, increasing its budget to 790,000 rupees per year and the staff to 6,600 men. Under Smith, the line saw many reforms and was officially named the Inland Customs Line in 1843.

Smith's new Inland Customs Line was first concentrated between Agra and Delhi and consisted of a series of customs posts at one mile intervals, linked by a raised path with gateways (known as "chokis") to allow people to cross the line every four miles. Policing of the barrier and surrounding land, to a distance of 10 to 15 miles (16 to 24 km), was the responsibility of the Inland Customs Department, headed by a Commissioner of Inland Customs. The department staffed each post with an Indian Jemadar (approximately equivalent to a British Warrant Officer) and ten men, backed up by patrols operating 2–3 miles behind the line. The line was mainly concerned with the collection of the salt tax but also collected tax on sugar exported from Bengal and functioned as a deterrent against opium, bhang and cannabis smuggling.