planned an invasion of Siam itself. Next year, near the end of the rainy season on 14 October 1548, (13th waxing of Tazaungmon 910 ME), 12,000 strong Toungoo forces led by Tabinshwehti and Bayinnaung invaded Siam via the Three Pagodas Pass. The Burmese forces overcame Siamese defences, and advanced to the capital city of Ayutthaya. But they could not take the heavily fortified city. One month into the siege, in January 1549, Siamese counterattacks broke the siege, and drove back the invasion force. On retreat, the Burmese tried to take Kamphaeng Phet, but it too was well defended by Portuguese mercenaries. Fortunately for the Burmese, they caught two important Siamese nobles (the heir apparent Prince Ramesuan, and Prince Thammaracha of Phitsanulok) in some open fighting, and negotiated a safe retreat in exchange for the nobles in February 1549. Lower Burma (1550–1552) After Tabinshwehti was assassinated on 30 April 1550, the kingdom he and Bayinnaung had built up in the last 15 years instantly unravelled. Instead of acknowledging Bayinnaung as the next king, all the governors of the kingdom, including Bayinnaung's own kinsmen, set up their own fiefdoms. Bayinnaung then set out to reclaim the kingdom. Starting with a small army of 2500 loyal followers, Bayinnaung first attacked native city of Toungoo where his brother Minkhaung had proclaimed himself king. After a siege of four months, Minkhaung surrendered, and was pardoned by his brother. On 11 January 1551, Bayinnaung was formally proclaimed king. Bayinnaung then received tribute from fiefs throughout central Burma, and Martaban in the south. Only Prome and Pegu in Lower Burma remained defiant. Bayinnaung captured Prome on 30 August 1551 after a five months' siege. On 12 March 1552, Bayinnaung defeated Pegu's ruler Smim Htaw in single combat on elephants, and the victor's forces brutally sacked the city. Confederation of Shan states (1554–1557) The Confederation-controlled Ava was next. Bayinnaung made extensive preparations, assembling a large invasion force (18,000 men, 900 horses, 80 elephants, 140 war boats). In December 1554, the Toungoo land and naval forces invaded. Within a month, the invasion forces held complete command of the river and the country. On 22 January 1555, the southern forces took the city. Bayinnaung then planned to follow up to the Confederation's home states to prevent future Shan raids into Upper Burma. With the entire Irrawaddy valley under his control, he was able to raise a large army of 24,000