Fortifications of Bangkok

The fortifications of Bangkok consist of several series of defensive structures built to protect the city during the late Ayutthaya to early Rattanakosin periods. The earliest structures were built when Bangkok was an outpost of Ayutthaya guarding entry to the Chao Phraya River during the 15th–16th centuries. These were reinforced when the city became the site of the short-lived capital of Thonburi after the fall of Ayutthaya in 1767. New walls and forts were built when the city of Rattanakosin replaced Thonburi in 1782, which were mostly removed and replaced in the second half of the 19th century in order to accommodate the expanding city. Today, four of the city's defensive forts remain, along with two short sections of the Rattanakosin city wall and one of the city gates.
History.
Ayutthaya and Thonburi.
As an important outpost guarding the Chao Phraya, Bangkok (then located on the west bank of the river) was protected by city walls. A pair of forts were located at the confluence of the old river channel and the new main channel excavated around 1538, straddling the new channel. Western maps of the late 17th century show the city wall in a rectangular shape, with the western fort as a cavalier raised over the southeast corner. Two smaller bastions protected the northwest and southwest corners.
Around 1685–1687, the French-oriented King Narai commissioned the construction of Western-style bastion forts to replace them. Construction was overseen by French engineer de la Mare, but only the eastern fort had been completed when resentment of the French's growing influence led to the Siamese revolution of 1688. The French garrison holding the fort was besieged by Siamese troops for four months before being allowed to retreat, and the fort was subsequently demolished during the reign of Phetracha, who usurped the throne.
Following the fall of Ayutthaya in 1767, the newly declared King Taksin established his capital at the site of Bangkok, to be known as the Thonburi Kingdom. He extended the city proper northward as far as Bangkok Noi Canal (part of the old river channel), and had a moat dug to protect the city's western flank. The city was also extended to the eastern bank, with a moat also creating an island on the eastern side. The city walls were rebuilt along the newly created moats. The old fort on the western bank of the river was renamed Wichaiprasit (), and became part of the Thonburi royal palace.
Early Rattanakosin.
Taksin was overthrown in 1782, and the new King Phutthayotfa Chulalok (Rama I) reestablished the capital as Rattanakosin, moving the city proper to the river's eastern bank. He had new outer moats dug, creating what is now known as Rattanakosin Island. He had the new fortifications rebuilt along these new boundaries, using materials salvaged from Taksin's old city walls and the ruins of King Narai's old fort, as well as the ruins of Ayutthaya's fortifications.
Rama I's city walls measured in length, encircling an area of . Fourteen defensive forts were built along the walls, and 63 gates provided access to the walled city. Each of the forts was named, and are as follows (from northernmost, in clockwise fashion):
Of the 63 city gates, 16 were tower gates with pointed roofs. The rest were simple doors in the wall. All the gates bore enchantments warding off evil spirits, except for the gate known as Pratu Phi (, "Ghost Gate"), which was used to transport dead bodies out of the city. The Ghost Gate was left unenchanted in order to allow the spirits of the dead to pass. To prevent evil spirits entering, it was situated in the direct line of sight of the Emerald Buddha, enshrined on the other side of the city in the royal temple of Wat Phra Kaew.
Rama I's fortifications were built to address traditional defence concerns, especially the lingering threat of a Burmese invasion that continued on for several decades. However, they never came into actual military use, as the Burmese threat ended following the Anglo-Burmese Wars and Britain's colonization of Burma.
1852 forts.
By the mid-19th century, Rattanakosin's walled city had become overcrowded, and King Mongkut (Rama IV) ordered the construction of Phadung Krung Kasem Canal in order to expand the city limits. Eight new forts were built in 1852 to guard the new boundary: seven along the canal, and one on the opposite bank of the river to the canal's mouth. Defensive walls, outdated by then, were no longer built.
The eight new forts received rhyming names. From south to north, they are:
Demolition and preservation.
Bangkok underwent rapid modernization beginning in the late 19th century, and by the 1920s most of the city's original forts and walls had been demolished to make way for the construction of roads and buildings. During the reign of King Prajadhipok (Rama VII, 1925–1935), the Royal Society resolved to preserve the two remaining original forts, Phra Sumen and Mahakan, for their historical value.
Today, Four of Bangkok's defensive forts remain, one of which is still in military use. Wichaiprasit Fort, the oldest, is now owned by the Royal Thai Navy. Phra Sumen Fort and Mahakan Fort are under the care of the Bangkok Metropolitan Administration (BMA), and part of Pong Patchamit Fort is preserved behind the Khlong San District Office. In addition, a section of the city wall is preserved in front of Wat Bowonniwet, and another section remains connected to Mahakan Fort. These structures, as well as the canals that formed the city moats, are listed as registered ancient monuments.
Present structures.
Wichaiprasit Fort.
Wichaiprasit Fort () is now part of the Royal Thai Navy Headquarters. The fort, along with the royal palace of Thonburi, had been given for the establishment of the Royal Thai Naval Academy in 1903, and became home to the Navy's headquarters after the academy relocated in 1946. A gaff-rigged flagpole was erected in 1971, and has since been used to fly the Naval Ensign. The fort has been used ceremonially for the firing of gun salutes since 1979, when Memorial Bridge was permanently lowered, preventing warships from sailing upriver to perform the task.
Phra Sumen Fort.
Phra Sumen Fort is the northernmost of Rattanakosin's original forts, located at the mouth of Khlong Rop Krung (the moat) where it meets the river, today the corner of Phra Sumen and Phra Athit Roads (). The octagonal fort is built of masonry on a -deep spread footing foundation. It is in diameter, and has a height of measured to top of the "sema"-shaped battlements of the upper level. The fort has rectangular battlements on the lower level, and is topped by a roofed heptagonal tower, which collapsed sometime during the reigns of kings Rama V to Rama VII and was rebuilt in 1981 to celebrate the bicentennial of the city's foundation. The surrounding area was subsequently developed into Santichaiprakan Park, which opened in 2000.
Mahakan Fort.
Mahakan Fort is the easternmost fort of Rattanakosin's walls, now situated next to Phan Fa Lilat Bridge of Ratchadamnoen Avenue and the junction of Khlong Maha Nak (the beginning of Saen Saep Canal) and Khlong Rop Krung (). The fort, also octagonal in shape and in three levels, has a diameter of and a height of , measured to the roof of the octagonal tower. Mahakan Fort has rectangular battlements on both its lower and upper levels, while the connected -long section of the city walls features "sema"-shaped battlements. The fort and walls were also restored in 1981 for the city's bicentennial.
Near Mahakan Fort, between the city wall and the canal, lies an old community whose wooden houses serve as an example of historic vernacular architecture. The community has been engaged in a decades-long struggle against eviction by the BMA, which intends to develop the area as a public park. Although agreements had been made in the 2000s to preserve and develop the neighbourhood as a living museum, the deals later broke down, and the BMA began demolishing houses whose owners accepted compensation in 2016. Other residents are still resisting eviction as of 2017, and there are still hopes that some of the buildings will be preserved. As of April 2018, all remaining residents have been evicted, and plans are underway to tear the remaining buildings down. However, the Mahakan Fort Community’s Facebook page has announced an initiative to create an online database about the Mahakan Fort community, and is crowdsourcing information about the site. In July 2018, BMA was completely developed surrounding area of Mahakan Fort to become a public park and the fort exhibition. 
City wall in front of Wat Bowonniwet.
Another section of the city wall, in length, along with a tower gate, remains in front of Wat Bowonniwet (). The wall here is thick and high. Also featuring "sema"-shaped battlements, steps beside the gate provided access to the top of the wall. The gate's pointed roof, which had earlier collapsed, was rebuilt in 1981 using photographic evidence from the reign of King Rama V.
Pong Patchamit Fort.
Pong Patchamit Fort is the only remaining of those built in 1852–1854 to guard Phadung Krung Kasem Canal. In contrast to the earlier forts which were towers in the city wall, these were large star-shaped forts similar to those of Western design. Pong Patchamit Fort is situated on the west bank of the river, today in Khlong San District (). It guarded the river together with the opposite Pit Patchanuek Fort, and fired gun salutes welcoming royal envoys during the time of King Mongkut. During King Chulalongkorn's reign, the Marine Department began flying signal flags from a pole installed at the fort.
Today, only a small section of the fort remains (an estimated area of out of the original ).
While official requests to scrap the fort for materials were documented as early as 1907, these were initially rejected, and it is unknown when the partial demolition took place. The site remains under the authority of the Marine Department, while the Khlong San District Office building now occupies part of the fort's former area.