Next year, in October 1548, three Burmese armies led by King Tabinshwehti and his deputy Bayinnaung invaded Siam through the Three Pagodas Pass.

But the Burmese negotiated a safe retreat in exchange for the return of two important Siamese nobles (the heir apparent Prince Ramesuan, and Thammaracha of Phitsanulok) whom they had captured.

The next Burmese invasion in 1563 would force a Siamese surrender in February 1564, and make Ayutthaya a vassal state of Burma for the first time.

By the early 15th century, Ava's former vassals—Mohnyin (and its allies Confederation of Shan States) in the north and the Prome Kingdom (Pyay) in the south—were regularly raiding their former overlord's territory with increasing frequency and intensity.

[9] During this period of tumult, Mingyi Nyo, then governor of Toungoo (Taungoo), a small region located at the southeastern corner of Ava Kingdom also declared independence in 1510, and largely stayed out of the internecine fighting in the following years.

When Ava fell to the combined forces of the Confederation and Prome in 1527, many people fled to Toungoo, the only region in Upper Burma at peace.

Toungoo's stability continued to attract manpower from the surrounding regions, especially after 1533 when the Confederation sacked its erstwhile ally Prome.

On the eve of the Siamese war, in 1547, Toungoo controlled a Lower Burma region from Pagan (Bagan) in the north to Moulmein in the south.

Fernão Mendes Pinto, a contemporary Portuguese explorer, recorded a rumour alleging that Si Sudachan had poisoned her husband in order to take control of the throne, and perhaps to restore the fallen House of Uthong to power.

In support of these allegations, she had many prominent officials executed, including the aged and high-ranking Phraya Mahasena (Minister of Defence), and replaced them with her favourites.

[17] It was also recorded that she was heavily pregnant and soon gave birth to a daughter; unable to conceal this secret, she mounted a coup, removed her son and put her paramour on the throne.

As the usurper king, Si Sudachan and their infant daughter proceeded by royal barge, Khun Phiren Thorathep and his conspirators sprang an ambush, killing all three.

[21] One of his first acts was to appoint Khun Phiren Thorathep as King of Sukhothai (but as a vassal to himself) with a capital at the great fortified town of Phitsanulok.

[7][8] According to the Burmese chronicles, a Siamese force of 6,000 had occupied Tavoy (Dawei) in the Upper Tenasserim coast, which he considered his territory, by January 1547.

[note 4] A joint land-naval attack on Tavoy drove out the Siamese forces led by the Lord of Kanchanaburi to lower Tenasserim.

[21] Upon hearing of the Burmese invasion, Maha Chakkraphat mobilized his kingdom, then gathered his forces at Suphanburi, a town just west of Ayutthaya.

[30] About a month into the invasion, mid-November 1548,[note 5] the King of Burma then continued his march eastward, capturing the villages of Ban Thuan, Kaphan Tru, and Chorakhe Sam Phan.

[30] The Burmese continued their advance and captured the ancient town of Uthong as well as the villages of Don Rakhang and Nong Sarai and closing in on Suphanburi.

Accompanying him were his Chief Queen, Sri Suriyothai, and one of their young daughters, Princess Boromdilok, the two riding together on a smaller war elephant.

Fearing for the life of her husband, Queen Sri Suriyothai charged ahead to put her elephant between the King and the Viceroy, thereby blocking his pursuit.

[31][33] The Viceroy then engaged the Queen in single combat, fatally cleaving her from shoulder to heart with his spear, also wounding her daughter—both mother and child met their deaths on the back of the same elephant.

The Chao Phraya basin where Ayutthaya is situated was low and prone to flooding—especially intense during the rainy season when torrential waters flowed in great quantity from the north along the Lopburi River.

Fifty Portuguese mercenaries, who had elected Galeote Pereira as their captain, defended the weakest part of the city wall for Maha Chakkraphat.

Thammaracha quickly mobilized his forces and with the help of the Governor of Sawankhalok, marched southward with a large army to attack the Burmese rear.

[8] Maha Chakkraphat saw the Burmese army's retreat as an opportunity take advantage of their weakness, so he ordered Prince Ramesuan and Thammaracha to follow and harass the enemy out of Siamese territory.

[38][39] According to the Burmese records, the Siamese king also agreed to provide an annual gift of 30 elephants, a token sum of money, and certain custom duties.

It was only in 1562 that Bayinnaung made an emphatic claim on the region by setting up a Burmese garrison at Tavoy,[note 7] in preparation for his invasion of Siam a year later.

The temple, which still exists, is known as Wat Suan Luang Sop Sawan [th] (วัดสวนหลวงสบสวรรค์) and the stupa is called Chedi Phra Sri Suriyothai [th] (เจดีย์พระศรีสุริโยทัย).

[44] All the facts pertaining to her life were taken from fragments of the Siamese royal chronicle the Annals of Ayutthaya and an account by Domingos Seixas, a Portuguese explorer.

[37] The war, beginning with the death of Chairacha, was dramatized in the 2001 Thai historical drama The Legend of Suriyothai, directed by Mom Chao Chatrichalerm Yukol.