The Nine Armies Battlefield Historical Park, located to the west of Kanchanaburi is a memorial to the Burmese–Siamese War (1785–1786), known as the Nine Armies' Wars in Siamese history because the Burmese came in nine armies, was fought between the Konbaung dynasty of Burma and the Chakri dynasty of resurgent Siam (Thailand).
In early 1785, King Bodawpaya of the Konbaung dynasty sent an expedition force to take Jung Ceylon (Phuket) to prevent foreign arms shipments to Siam but the invasion force was driven back. In October 1785, Bodawpaya pursued an ambitious campaign to expand his dominions into the lands of the former Ayutthaya Kingdom. He launched a four-pronged invasion towards Chiang Mai, Tak, Kanchanaburi, and Jung Ceylon. The combined strength was about 50,000 men. The invasion forces had faced tough heavy resistance from the Siamese forces and finally the war became a total disaster for the Burmese armies. The defeat that the invasion turned out to be, became the last full-scale invasion of Siam by Burma.
The historical park was created by the Royal Thai Army to commemorate the bloody battles that took place in Kanchanaburi Province.

Source: Wikipedia