them at the same nominal value, a process known as debasement. At the ascent of Nero as Roman emperor in AD 54, the denarius contained more than 90% silver, but by the 270s hardly any silver was left. By diluting the silver with other metals, the government could issue more coins without increasing the amount of silver used to make them. When the cost of each coin is lowered in this way, the government profits from an increase in seigniorage. This practice would increase the money supply but at the same time the relative value of each coin would be lowered. As the relative value of the coins becomes lower, consumers would need to give more coins in exchange for the same goods and services as before. These goods and services would experience a price increase as the value of each coin is reduced. Ancient China Song dynasty China introduced the practice of printing paper money to create fiat currency. During the Mongol Yuan dynasty, the government spent a great deal of money fighting costly wars, and reacted by printing more money, leading to inflation. Fearing the inflation that plagued the Yuan dynasty, the Ming dynasty initially rejected the use of paper money, and reverted to using copper coins. Medieval Egypt During the Malian king Mansa Musa's hajj to Mecca in 1324, he was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels. When he passed through Cairo, he spent or gave away so much gold that it depressed its price in Egypt for over a decade, reducing its purchasing power. A contemporary Arab historian remarked about Mansa Musa's visit: "Price revolution" in Western Europe From the second half of the 15th century to the first half of the 17th, Western Europe experienced a major inflationary cycle referred to as the "price revolution", with prices on average rising perhaps sixfold over 150 years. This is often attributed to the influx of gold and silver from the New World into Habsburg Spain, with wider availability of silver in previously cash-starved Europe causing widespread inflation. European population rebound from the Black Death began before the arrival of New World metal, and may have begun a process of inflation that New World silver compounded later in the 16th century. Measures Given that there are many possible measures of the price level, there are many possible measures