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.

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 (Thai: ป้อมวิไชยประสิทธิ์), and became part of the Thonburi royal palace.

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 7.2 kilometres (4.5 mi) in length, encircling an area of 2,589 rai (4.142 km²; 1.599 sq mi). 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 (ประตูผี, "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.