Tai peoples who originally lived in southwestern China, migrated into mainland Southeast Asia over a period of many centuries. The oldest known mention of their existence in the region by the exonym Siamese is in a 12th century A.D. inscription at the Khmer temple complex of Angkor Wat in Cambodia, which refers to syam, or "dark brown" people. It was believed that Siam derived from the Malay word sagûm, or brown race, with a contemptuous signification. During the reign of Rama III (1824–1851,) a Scottish trader had experimental coins struck in England at the king's behest, Though not adopted for use, the name of the country put on these first coins was Muang Thai, not Siam.