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Accounts vary on the origin of Prasat Thong. While traditional Thai historians hold that he was an illegitimate son of King Ekathotsarot, Jeremias van Vliet's account states that he was the maternal cousin of King Songtham – his father was Okya Sri Thammathirat (Thai: ออกญาศรีธรรมาธิราช), elder brother of the mother of King Songtham. He was born during the reign of King Naresuan around 1600 and was known to cause mischief in the royal court. He ruined the palace Agricultural Initiation Ceremony and was threatened with execution; only pleas from the queen of King Naresuan won a reduction of the punishment to life imprisonment. He was later pardoned and given the title of Okya Sri Vorawong (Thai: ออกญาศรีวรวงศ์) – a high ranking title of royal page.
Rise to power
The rise of Prasat Thong to power was documented in van Vliet’s The Historical Account of the war of Succession following the death of King Pra Interajatsia (1650). As the king's maternal cousin, he held great influence. It is said that he was a very ambitious prince and wanted to become a king. King Songtham had had his brother Prince Sri Sin as the Front Palace, technically his successor, but a palace faction including Prasat Thong persuaded the king to give the throne instead to his son Prince Chetthathirat. When King Songtham died in 1628, Chetthathirat ascended the throne and a great purge of the mandarins who had supported Prince Sri Sin was instigated, including the Samuha Kalahom or Defence Minister. Prasat Thong then replaced him as the Defence Minister with the new title of Okya Suriyawong (Thai: ออกญากลาโหมสุริยวงศ์).
Prasat Thong had Yamada Nagamasa, the head of Japanese mercenaries then known as Okya Senaphimok (Thai: ออกญาเสนาภิมุข), as a supporter. Prince Sri Sin escaped into monkhood to save his life. However, he was lured into the palace with his monastic robes off and with princely attire. He was arrested and then exiled to Phetchaburi where he was thrown into a well to be starved to death. The prince was narrowly saved by the local monks who thrown a body into the well as substitute. Prince Sri Sin then organized a rebellion in Petchaburi. Prasat Thong sent Okya Kamhaeng and Yamada Nagamasa to lead the Japanese troops to crush down the rebels. Prince Sri Sin was captured and executed in Ayutthaya.
With the Prince Sri Sin gone, Prasat Thong was in full power. In 1629, his father died. The funeral was held in grandeur and his father’s ashes were cremated twice – a practice reserved for royalty. On that day King Chetthathirat called for an audience with all the nobles but all of them had gone to the funeral – much to the king’s great anger. The king threatened to punish Prasat Thong but Okya Phraklang (the Minister of Trade who was Prasat Thong's ally) managed to calm the king and convince him of Prasat Thong's innocence. The king was unprepared when Prasat Thong hurled armies into the palace. The king fled but was captured and executed. Prasat Thong installed the king’s brother – the eleven-year-old Prince Athittayawong – as the new puppet king with Prasat Thong as the regent who crowned himself as the second king.
Prasat Thong strived to eliminate his allies-turned-rivals – the Okya Kamhaeng who contested him for the throne and Yamada Nagamasa who objected to the takeover of the throne by Prasat Thong. He quickly condemned Okya Kamhaeng to treason and execution followed. And he sent Okya Senaphimok south as the governor of Ligor, away from Ayutthaya. As soon as the Japanese mandarin left the city, only about a month after his ascension, the child-king was deposed and subsequently executed. Okya Suriyawong crowned himself as the full-fledged King of Siam. Upon arriving at Ligor, Okya Seniphimok heard of the coup at Ayutthaya and rebelled. However, he was poisoned to death through his wounds by an agent sent by the new king.
As a powerful and decisive leader, he promulgated many criminal laws and sometimes, according to Van Vliet, he even executed prisoners by himself.
Siam was a major trading center attracting Europeans merchants. Prasat Thong was interested in controlling the towns in the southern peninsula, perhaps because of profits from overseas trade. Ayutthaya lost northern subjugated principalities such as Chiangmai.
His son, Narai, eventually began a significant relationship with European countries.
- The Royal Institute. List of monarchs Ayutthaya. (Thai)