Ubon Ratchathani, commonly shortened to Ubon, is a city in northeastern Thailand and the administrative centre of Ubon Ratchathani Province. It is one of the four largest cities in Isan, alongside Nakhon Ratchasima, Udon Thani, and Khon Kaen, collectively known as the "big four of Isan." The city lies on the north bank of the Mun River, approximately 497 km (309 mi) from Bangkok in a straight line, or around 629 km (391 mi) by road.