Thonburi (Thai: ธนบุรี) is a vast district that consists of the entire west bank of the Chao Phraya river in Bangkok. After the sack of Ayutthaya in 1767, General Phraya Taksin made Thonburi the new capital of Siam for a chief period of time. It is hard to believe this was once the country's capital, as the district is devoid of the grand structures seen in other former capitals. In fact, Thonburi stayed relatively isolated from Bangkok proper, and for centuries was an agricultural land filled with canals and fruit orchards. While Thonburi has quickly developed in recent decades, most visitors still come here for the cool and peaceful atmosphere. The traditional Thai way of life on the canals still exists here, as do the floating vendors and orchard farms.

Originally, "Bangcok" referred to a village in the area that today roughly corresponds to the neighborhoods of Bangkok Noi and Bangkok Yai. At that time, the Chao Phraya river had a completely different course than it does today. The Chao Phraya had a horseshoe shape that is similar to the current course of the Bangkok Noi and Bangkok Yai canals. One theory on the origin of the name is that Bangcok came from "Bang Ko", which means "island village" in Thai, referring to the village that was almost completely surrounded by the Chao Phraya river. Bangcok was the first part of Thonburi to be settled, as its location was a convenient storage point for trade ships that sailed north towards Ayutthaya. The horseshoe shape of the Chao Phraya river slowed down trading ships, and in 1542, a small canal was dug across the base of the meander to shorten sailing time. The strength of the current eroded the canal's banks, and over time the new canal became the main course of river. Bangcok was on the east bank of the old course of the river, but on the west bank of the new course.

As sailing times fastened, Bangcok became a tax collecting port and customs office for foreign traders sailing to Ayutthaya. In 1665, King Narai the Great ordered the construction of Vichaiyen Fort near the mouth of the Bangkok Yai canal to protect Ayutthaya from foreign invasions. This fort is now known as the Vichaiprasit Fort and can still be seen from the Chao Phraya Express Boat today. With it, the village got the status of fortified city and was renamed Thonburi. When the city of Ayutthaya was burnt down to the ground by Burmese armies in 1767, General Taksin was in charge of the resistance. A capable military leader, he conquered back Siam within a year and took hold of large parts of Southeast Asia in the following decade. He became King of Siam and established Thonburi as the new capital of the country. He created his palace close to the fort, while the residence of General Phraya Chakri (who would later become King Rama I) was near the current location of Wat Rakhang.

In 1779, King Taksin had proclaimed himself a sotapanna (or divine figure), striking against the will of the powerful Buddhist monkhood. The state was in economic turmoil, there was rampant corruption and famine struck the country. King Taksin tried to maintain order with harsh punishment and purges. When General Phraya Chakri was fighting out a war with Cambodia, a rebellion took hold of Thonburi, forcing King Taksin to step down. Shortly after, he was secretly executed. When General Phraya Chakri returned, he was offered the throne and became King Rama I, the first King of the Chakri dynasty. He made Rattanakosin the new capital of Siam, as he believed that city would be easier to defend against foreign invasions. This was the end of a brief era now known as the Thonburi Period. It wasn't the end of "Bangcok" — foreigners never adapted to the changes and kept using the name, even for the eastern bank of the Chao Phraya river while that is technically incorrect.

Thonburi stayed relatively undeveloped, especially compared to its neighbor at the other side of the river. The economy was mostly agricultural-based with fruit orchards crisscrossed by canals. Many durian species have originated in Thonburi, including mon thong, chanee and kan yao. Most of the fruit orchards have disappeared as Thonburi became more developed. It wasn't until 1932 when Thonburi became physically linked to Bangkok for the first time with the construction of the Memorial Bridge. Thonburi's distinct identity only held out for forty more years, when it was incorporated into the city of Bangkok in 1971.