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The Phraya Phasim Campaign and the Chiang Mai Army, Late 1584
Only a few months after the declaration of independence, King Nanda Bayin sent two armies to punish Ayutthaya. One, under Phraya Phasim, came in through the Three Pagodas Pass; the other, from Chiang Mai, came down from the north. Naresuan defeated them one at a time before they could join forces, which made this campaign the first real test of the newly won independence.
The ≈ sign marks an approximate location. Borders on the map are modern and shown for orientation only. Campaign routes are approximate lines drawn from the chronicles and modern studies, not the exact path taken. Dashed lines are enemy armies.
Preparing for war
After returning from Mueang Khraeng, Naresuan expected that Hanthawaddy would certainly send an army, so he moved people from the northern towns down to Ayutthaya, both to add manpower to the capital and to stop the enemy from using those towns as a source of supplies.
An English-language encyclopedia summarising these events says he first secured Sukhothai and Sawankhalok, and then moved the people of the northern towns, families and all, down to Ayutthaya.
Hanthawaddy's two armies
According to the royal chronicles, Phraya Phasim, lord of Bassein in Lower Burma, led about 30,000 men in through the Three Pagodas Pass, past Kanchanaburi and on towards Suphanburi.
The second force was the Chiang Mai army, which the chronicles put at about 100,000 men. It came south both overland and by river as far as Chainat, then sent part of its strength to set up camp at Pak Nam Bang Phutsa. Troop numbers in the chronicles are often inflated, so they are best read as a general picture: the Chiang Mai army was much bigger than Phasim's.
Beating one army at a time
Naresuan chose to deal with Phraya Phasim's army first. He used cannon to block the enemy's advance around Khao Phraya Maen near Suphanburi, and Phasim's army broke, fled into the hills and forest, and retreated the way it had come.
Meanwhile the Chiang Mai army camped at Bang Phutsa was harassed again and again by guerrilla bands led by Phra Ratchamanu, until it finally had to withdraw north. The English-language encyclopedia sums it up the same way: the two armies were defeated separately before they could combine.
The Burmese sources tell it differently
The Burmese chronicles say that after the declaration of independence King Nanda Bayin was furious and quickly raised an army of about 7,000 men, with the Crown Prince Mingyi Swa as one of its commanders. But the army had been prepared in a hurry and arrived in the rainy season, so it was caught in the floods of the Chao Phraya basin and attacked by Siamese war boats until it was almost wiped out.
The Burmese figures are far lower than the Thai ones, and they do not describe two separate armies as the Thai chronicles do. On the essentials, though, both sides agree: the army sent to punish Ayutthaya was defeated and turned back.
What this campaign meant
This victory showed that Ayutthaya was truly able to defend its independence. Using cannon to block an advance, beating enemy armies one at a time and sending guerrilla bands to harass them are tactics that, according to the chronicles, appear again and again in the campaigns that followed.
Reading the route on the map
The line on the map shows the route of Phraya Phasim's army (the enemy) from the Three Pagodas Pass through Kanchanaburi to Suphanburi. The Kanchanaburi point uses the present-day town, which was moved to its current site in the reign of King Rama III, and the exact location of Khao Phraya Maen is still unknown. The Chiang Mai army at Chainat and Bang Phutsa is not shown on this line.
Waypoints along the route
| Waypoint | Coordinates | Notes |
|---|---|---|
| 1. Three Pagodas Pass | 15.302, 98.402 | |
| 2. Kanchanaburi | 14.019, 99.531 | Approximate location. Uses the coordinates of the present-day town, which was moved here in the reign of King Rama III; Ayutthaya-period Kanchanaburi stood at a different spot. |
| 3. Suphanburi | 14.467, 100.117 |
Where historians still disagree
- Army sizes: the Thai chronicles give 30,000 men for Phasim's army and 100,000 for the Chiang Mai army, while the Burmese chronicles record the army sent after the declaration of independence as only a few thousand. The figures differ many times over, so they should be used with caution.
- The shape of the campaign: the Thai chronicles describe two armies beaten separately at Suphanburi and Bang Phutsa; the Burmese chronicles describe a single army caught in the floods and attacked by Siamese war boats.
- Battlefield locations: Khao Phraya Maen and Pak Nam Bang Phutsa are names from the chronicles, and no present-day location has yet been confirmed for either.
Frequently asked questions
Who was Phraya Phasim?
He was the lord of Bassein in Lower Burma, whom King Nanda Bayin sent to lead one of the two armies against Ayutthaya in late 1584, and again in 1590.
Where was the Phraya Phasim campaign fought?
Phraya Phasim's army was routed around Khao Phraya Maen near Suphanburi, while the Chiang Mai army camped around Chainat and Pak Nam Bang Phutsa before it was harassed into retreating.
Last updated 10 November 2026