20 pesos 15 g pure GOLD 1959: OBVERSE: Writing obverse: ESTADOS UNIDOS MEXICANOS. Description obverse: Eagle standing on one leg over a cactus, killing a snake, beneath them there is a lake surrounded by two composed branches ; in the central part of the coin is displayed the year it was minted. Translation obverse : (United States of Mexico). REVERSE: Writing reverse: VEINTE PESOS/ *15 g. ORO PURO*. Description reverse : Stone of the sun or 'Aztec calendar'. Translation reverse : (Twenty pesos/15 g pure gold). HISTORY: MEXICO - REPUBLIC (after 1911) The Mexican Constitution was voted in 1917. The Revolution — with the opposition of the revolutionaries Pancho Villa, Emilio Zapata, Huerta and Carranza — was not over until 1923. The reformist policy lasted until 1940, when Trotski was murdered in Mexico. The industrialization developed strongly as of 1945 and by 1970 Mexico was part of the head group of developing countries. During the 1980s, the economy went down and several deflations took place. In 1992, Mexico signed the NAFTA (North American Free Trade Agreement) together with Canada and the United States. It came into force in 1994.