Text & photographs by Tricky Vandenberg - February 2010
Updated April 2020
(At the lower end of the City appears a large bastion
The first is furnished with cannons against the ships
coming up. To fence the city wall against the wasting
of the current, a narrow bank, or key is left, which is
built upon in many places. [Kaempfer])
View of a part of Pom Phet
View of Phet Fortress from the confluence
Pom Phet on Vingboons' Iduea painting
Pom Phet on de Courtaulin' s map
Pom Phet on Kaempfer's map
(Pom Phet on Vingboons' Iduea painting)
(Pom Phet on de Courtaulin' s map)
Photographs by Somchai Pattanavaew & Tricky Vandenberg
(View of Phet Fortress from the confluence)
(View of a part of Pom Phet)
Pom Phet or the Diamond Fortress was one of the sixteen fortresses along the city
walls of Ayutthaya. Situated in the southeast, at the confluence of the Pa Sak River and
Lopburi River (today the Chao Phraya River) in Bang Kaja area (1) and on the east
bank of the
Nai Kai canal,

Pom Phet was the most important fortress, protecting the harbour where foreign ships
were forced to anchor for inspection and unloading. No foreign ships travelling up the
Chao Phraya River before were allowed beyond this point. In 1767, the Burmese were
unable to penetrate Ayutthaya from this fort. The city walls were finally breached on the
northeast side of the main island at the Maha Chai fortress to be exact. Pom Phet is one
of the two remnants of old fortresses and now a public park. The site has been recently
renovated since serious damage occurred from water erosion to the river banks.

Prince Damrong situates the construction of Pom Phet and
Pom Sat Kop (a fortress in
the north-west of the city) during the reign of King Maha Chakkraphat (r. 1548-1569),
shortly after the first attack of Ayutthaya by the Burmese in 1549 [1]. King Chakkraphat
realized that Ayutthaya had entered the age of the gunpowder and large guns came to
dominate the war theater and thus strengthened the defenses of the city by a series of
construction works: city walls were reinforced and redone in brick (brick does not
shatter on impact from a cannon ball as stone does); a new northern moat was dug to
protect the northern part of the city - the
Maha Nak Canal; and walled fortresses were
built along the city wall, mostly at waterway intersections. [1]

Ayutthaya was conquered in 1569 and became temporarily a vassal state of Burma.
King Maha Thammaracha (r.1569-1590) was allowed to build new walls around the city
under the pretext of a threat from Cambodia (1570). The new walls were extended to
the riverbanks in 1580. [2] The moat by the front ramparts on the east, was dug 20 m
wide and 6 m deep from the
Maha Chai Fortress down to connect with Kaja Village [4]
(south of the city on the left bank of the Chao Phraya).

The original Phet fortress was circular shaped and probably constructed under the
architectural guidance of the Portuguese. The earliest drawing of the fortress is seen in the
Iudea painting from Johannes Vingboons, published around 1665, and likely based on
information dating from Jeremias Van Vliet's time. The fortress is clearly visible on the
painting with a round shape. Archaeological evidence indicates that the first walls were
up to 6.5 meters in width and consisted of brick and laterite, while the interior was filled
with rubble.

King Narai (r. 1656-1688) was very interested in the architectural skills of the Sicilian
Jesuit priest Tommasa Valguernera (2) and asked him to take charge of the rebuilding of
the walls and fortresses of Ayutthaya in 1663. Valguernera designed and superintended
the construction of new forts at Ayutthaya (3), Bangkok, Nontaburi, and other places,
primarily designed to counter the Dutch aggression. [5]

In 1685, the French engineer La Mare (3) arrived with the de Chaumont - de Choisy
embassy and remained at King Narai's request in order to build fortifications. He
designed fortifications for Ayutthaya (4), Lopburi (including Thale Chupson), Nakhon Sri
Thammarat, Songkhla, Phatthalung, Mergui and Inburi and implemented temporary
improvements to the fortifications of Bangkok. [6]

Likely the French built an hexagonal structure on the original foundation of Pom Phet (5).
This can be seen on de Courtaulin's map of 1686, showing the fortress with a more
rectangular outlook. The rounded shape of the old fortress created "dead" zones, which
sheltered attackers from defending fire. The round turret was extended into a diamond or
star-shaped fortress in order to improve its defense. Bastions were added to provide
covering fire from different angles. The name "Diamond Fortress" is either derived from
the shape of the fort, or from the ancient Greek word for Diamond - "adámas" meaning

On the ground floor of the fort, there were 16 large guns: eight placed in a portal and
eight more placed between the merlons of the battlement. [7] The fort had a second
floor, likely a kind of cavalier, a tower dominating the fort and the nearby countryside.
Next to the main fort were another three bastions - projecting parts of the fortress - built
against the line of the city wall covering the harbour area. This can be clearly seen on
Kaempfer's map of Ayutthaya.

Kaempfer in his work "The History of Japan" wrote:
At the lower end of the City
appears a large bastion advancing into the water, besides several small ones. The
first is furnished with cannons against the ships coming up. To fence the city wall
against the wasting of the current, a narrow bank, or key is left, which is built
upon in many places.

Most parts of the wall and the fortresses were dismantled in the reign of King Rama I,
who had the bricks taken to be used in the construction of the new capital in Bangkok.


(1) Bang Kaja was a Chinese settlement area and known for its water market opposite
the Pom Phet fortress. It was an area were Chinese and Cham sold sugar, sago small
grain and large grain, sulphate, red sandalwood, ratan gear and other goods.
(2) Father Tommaso Valguarnera, a Sicilian, arrived from Macau in 1655 and remained
in Siam for 15 years. In 1663 Father Cardosa was sent to Ayutthaya to take the place of
Valguarnera as superior, as the latter had been asked by King Narai to rebuild the walls
of Ayutthaya. Valguarnera rebuilt the city walls of Ayutthaya until 1670. He was
appointed Visitator of the Japanese and Chinese Provinces and left Siam. He returned
although to Siam in 1675 and again was occupied with rebuilding the walls of Ayutthaya
until his death in Ayutthaya in 1677. [3]
(3) One of the possible drafters of the Bellin Map. La Mare was initially embarked to
teach piloting to the marine guards of the embassy, and apparently was not a trained
engineer in France. Het was although a gifted self-made man and fell soon in the taste of
Constantine Phaulkon. On arrival of the second French Embassy in 1687 -  which was
carrying four "Ingenieurs du Roi" to the French general Desfarges - the works at the fort
in Bangkok were already ongoing. La Mare found him soon at loggerhead with Jean
Vollant des Verquains, one of the four engineers working in Siam in 1687-1688 [5].
(4) Brick fortresses were constructed, to replace the old fortifications. Known fortresses
were Pom Maha Chai, Pom Sat Kop, Pom Phet, Pom Ho Rachakhru and Pom Jampa
(5) Hexagonal shape ramparts are usually found in forts built by the French such as the
Lopburi and Bangkok fortresses built in the reign of King Narai.


[1]  Our Wars with the Burmese - Prince Damrong Rajanubhab (1917) - Re-edited
White Lotus (2001) - page 66.
[2] A History of Siam - W.A.R. WOOD (1924) - page 114.
[3] Ibid - page 128/130.
[4] The Royal Chronicles of Ayutthaya - Richard D. Cushman (2006) - page 82 /
Source: British Museum.
[5] The Jesuits In Thailand - Part I (1607) - 1767 by Pietro Cerutti, S.J.
[6] Three Military Accounts of the 1688 Revolution in Siam - Jean Vollant des
Verquains - translated by Michael Smithies (2002).
[7] Discovering Ayutthaya - Charnvit Kasetsiri & Michael Wright (2007) - page
[8] A History of Siam - W.A.R. Wood (1924) - page 273.