“The mountains are like the bones of the earth. Water is its blood,” wrote a Vietnamese geographer in 1820. Lowland Việt Nam is aquatic, but it is also multiregional and polyethnic. The country's three historic lowland regions are bounded by extensive uplands, all linked by interrelated landscapes, economies, and cultures. Throughout the plains, water plays a key role in the economy and communications. In the north and south, the Red River and the Mekong River form wide deltas and flow into the South China Sea. Linking the two deltas is the central region, many hundreds of miles of curving coastline, broken every twenty miles or so by river mouths and port towns.