The Bangkok forts were constructed after King Rama I established Bangkok as the new capital 1782. With the destruction of Ayutthaya by the Burmese in 1767 still fresh on his mind, security was a critical condition.

The new capital, though in a far more defensible position than the previous capitals, Thonburi, Ayutthaya and Sukhothai, had to be reinforced.

The defense of Rattanakosin rested on four elements: the Chao Phraya River, a major water obstacle; the canal rings which created a defensive belt of moats; the city walls and the Bangkok forts.

Lod Canal was already in existence, dug during the reign of King Taksin (1767 1782) when the capital was still in Thonburi. The canal was renamed Asadang Canal in 1982, after Prince Asadang, a son of King Chulalongkorn or King Rama V.

With the Chao Phraya River on the west and Lod Canal to the east, a second canal ring was dug in 1785 by 10,000 Khmer prisoners of war. This canal stretched from Banglampu in the north to the present Phra Pok Klao Bridge in the south and turned the old city into an island Rattanakosin Island.

The second canal ring was called Rob Krung (around the city). Today, this canal is called Banglampu Canal in the north and Ong-Ang Canal in the south.

A protective wall was erected along the canal. Fourteen Bangkok forts and observation towers along the Chao Phraya River and the Rob Krung Canal reinforced the city defenses. Unfortunately all that remains today are two forts, a section of the old city wall and an old gateway.

Of the two Bangkok forts that remain today, the first is Fort Phra Sumen to the north at the confluence of the Chao Phraya River and Banglampu Canal.

The second fort is Fort Mahakarn covering the Rob Krung Canal to the east, near Wat Saket the Temple on the Golden Mount. About 200 m of the old city wall along Maha Chai Road is still standing today and so is the old gateway.

From 1851 54, during the reign of King Rama IV, the third canal ring was built. This was the Padung Krung Kasem Canal, the longest of the three canal rings, stretching from Thewet in the north, past Hua Lam Pong Station to Bangrak in the south. This time, Chinese laborers dug the canal.

During the reign of the King Rama I, threats of invasion were still strong. The Bangkok forts and the canals provided the protection and security for the survival of the new capital, which has transformed to a modern metropolis today.

Find out what's behind the old wall at Fort Mahakarn the living legacy.