medium. The founder of the Yuan dynasty, Kublai Khan, issued paper money known as Chao in his reign. Chinese paper money was guaranteed by the State and not by the private merchant or private banker. The concept of banknotes was not brought up in the world ever since until during the 13th century in Europe, with proper banknotes appearing in the 17th century. The original notes during the Yuan dynasty were restricted in area and duration as in the Song dynasty, but in the later course of the dynasty, facing massive shortages of specie to fund their ruling in China, began printing paper money without restrictions on duration. Chinese paper money was therefore guaranteed by the State and not by the private merchant or private banker. Kublai and his fellow rulers encouraged trade between China and other Khanates of the Mongol Empire. During this era, trade between China and the Middle East increased, and many Arabs, Persians, and other foreigners entered China, some permanently immigrating. It was during this period that Marco Polo visited China. Although Kublai Khan wished to identify with his Chinese subjects, Mongol rule was strict and foreign to the Chinese. Civil service examinations, the traditional way that Chinese elites entered the government, was ended, and most government positions were held by non-Chinese, especially the financial administration of the state. Over-spending by Kublai and his successor caused them to resort to high taxes and extensive state monopolization of major sectors of the economy to fund their extravagant spending and military campaigns, which became a major burden on the Chinese economy. State monopolies were instituted in salt, iron, sugar, porcelain, tea, vinegar, alcohol and other industries. The most controversial of Kublai's policies, however, was opening the tombs of the Song emperors to gain treasure for the treasury, and issuing large amounts of notes which caused hyperinflation. These policies greatly conflicted with Confucian ideals of frugal government and light taxation. As a result of Kublai's policies, and the discrimination of the Mongols towards the Chinese, South China was beset by violent insurrections against Mongol rule. Many Chinese refused to serve or associate themselves with the Yuan administration, who they viewed as barbarian despots. During the 1340s, frequent famines, droughts, and plagues encouraged unrest among the Chinese. In 1351, a peasant rebel leader, who claimed he was the descendant of the Song Emperor Huizong, sought to restore the Song by