Thailand is located in the center of Southeast Asia, bordering Myanmar, Laos, Cambodia, and Malaysia. Before 1939 the country was known as Siam. Siamese states emerged in the trading roads between Chinese, Khmer and Malay. Kingdom of Sukhothai is the first prominent Thai state which existed from the 13th to 15th century in northern river plains. Then the Ayutthaya Kingdom in 14th century emerged and conquered Sukothai becoming the most powerful Thai state until its capital Ayutthaya was sacked by Burmese forces in 1767. Ayutthaya was known to Western Europeans as a marvellous city with around 1 million inhabitants. After the fall of Ayutthaya, King Taksin found a new capital at Thonburi on the west bank of Chao Phraya river plain. The new kingdom lasted for only 15 years when the military leader made the revolution against King Taksin and placed a king from a new dynasty, the Chakri Dynasty. Rama I then moved the capital to the east bank of the river and named the new capital as Krung thep. Bangkok is the common name known by the westerners since it was the trading posts of various western merchants from Ayutthaya time. Baht, a unit of weight of about 15 grams, has been the currency unit since Sukhothai time, along with the Cowry shells called Bia. Silver coins, hammered into ring-shaped in Sukhothai period, are called Podduang. In Ayutthaya period, bullet coins have a more round shape, and private production of bullet coins is banned. Ayutthaya-style bullet coins are produced until Rama IV, when the trade barrier between commoners and foreigners is abolished, the rapid economic growth making production of bullet money insufficient. Coinage revolution is undertaken by Rama IV who ordered minting machine from the British and built a new mint in the Grand Palace. In the late reign of Rama V, the traditional binary subunit of Baht is decimalized, with a Satang equaling 1/100 Baht. The bullet coins are demonetized due to high rate of counterfeits. In Rama VI reign, all pre-decimal coins are demonetized. In the long reign of Rama IX, many commemorative coins are produced and circulated along with the standard coins. Baht is one of the strongest currencies in the region.