used as an early form of money. In the Aztec Empire, under the rule of Montezuma cocoa beans became legitimate currency. Currency was introduced as standardised money to facilitate a wider exchange of goods and services. This first stage of currency, where metals were used to represent stored value, and symbols to represent commodities, formed the basis of trade in the Fertile Crescent for over 1500 years. Numismatists have examples of coins from the earliest large-scale societies, although these were initially unmarked lumps of precious metal. Trends Doha rounds The Doha round of World Trade Organization negotiations aimed to lower barriers to trade around the world, with a focus on making trade fairer for developing countries. Talks have been hung over a divide between the rich developed countries, represented by the G20, and the major developing countries. Agricultural subsidies are the most significant issue upon which agreement has been the hardest to negotiate. By contrast, there was much agreement on trade facilitation and capacity building. The Doha round began in Doha, Qatar, and negotiations were continued in: Cancún, Mexico; Geneva, Switzerland; and Paris, France, and Hong Kong. China Beginning around 1978, the government of the People's Republic of China (PRC) began an experiment in economic reform. In contrast to the previous Soviet-style centrally planned economy, the new measures progressively relaxed restrictions on farming, agricultural distribution and, several years later, urban enterprises and labor. The more market-oriented approach reduced inefficiencies and stimulated private investment, particularly by farmers, which led to increased productivity and output. One feature was the establishment of four (later five) Special Economic Zones located along the South-east coast. The reforms proved spectacularly successful in terms of increased output, variety, quality, price and demand. In real terms, the economy doubled in size between 1978 and 1986, doubled again by 1994, and again by 2003. On a real per capita basis, doubling from the 1978 base took place in 1987, 1996 and 2006. By 2008, the economy was 16.7 times the size it was in 1978, and 12.1 times its previous per capita levels. International trade progressed even more rapidly, doubling on average every 4.5 years. Total two-way trade in January 1998 exceeded that for all of 1978; in the first quarter of 2009, trade exceeded the full-year 1998 level. In 2008, China's two-way trade totaled US$2.56 trillion. In 1991 China joined the Asia-Pacific Economic Cooperation group, a trade-promotion forum.