Thonburi was originally the locals and foreigners are called “Bangkok” in the Royal Chronicle (AD 2091-2111), called “Thonburi Sri Samut” is Phra Nakhon and Thonburi in currently, it is the Chao Phraya River delta that was abundant with various canals. There are various canals scattered throughout the area. Chao Phraya River flows since Nonthaburi the winding down to Phra Nakorn. In the reign of Phra Chai Racha Thirat (AD 2077-2089) was ordered to dig canal shortcuts to connect Chao Phraya River that flows through the Bangkok Noi canal passes to Bangkok Yai. The city became an important strategic outpost and a marine outpost. Thonburi have trade with foreign countries the great flourished in the reign of King Narai (AD 2199-2231). He ordered to build a fort on both sides of the river to prevent the enemy from the sea given name “Pom Wichai Yen”.