A salt tax refers to the direct taxation of salt, usually levied proportionately to the volume of salt purchased. The taxation of salt dates as far back as 300BC, as salt has been a valuable good used for gifts and religious offerings since 6050BC. The salt tax originated in China, in 300BC and became the main source of financing the Great Wall As a result of the successful profitability of the Salt Tax, it began filtering through the rulings of nations across the world, France, Spain, Russia, England and India were the main regions to follow the Chinese lead. Salt was used as a currency during the Roman Empire and towards the end of their reign, the Romans began monopolising salt in order to fund their war objectives. Salt was such an important commodity during the Middle Ages that governments would often incorporate the salt trade as a state enterprise. Salt is one of the longest standing sources of revenue for governments, the taxation policy was so successful due to the vital role of salt within the human diet. Salt Taxing has been extremely influential in many of the political and economic revolts within history, resulting in important historic events including the French Revolution, the Moscow Salt Riot, the Salt March in India, and the Salt Tax Revolt in Spain.