Cầu River (Vietnamese: Sông Cầu) is a river of northern Vietnam. It flows through the provinces/cities of Bắc Kạn, Thái Nguyên, Bắc Giang, Hanoi, Bắc Ninh. It begins at the Phia Bioóc Peak in Chợ Đồn District, west of mountainous province of Bắc Kạn.
The river has a length of 288 km and basin area of 6,030 km².
Thái Bình river (Vietnamese: Sông Thái Bình) is the name of the Thái Bình river system's main river in Northern Vietnam. This river system joins with the Red River system and brings alluvium to create Red River Delta.
Thái Bình river starts in the area of Đồng Phúc commune, Yên Dũng District, Bắc Giang Province – where the Thuong River and Cầu River join with each other. It then flows to Hải Dương Province and becomes the boundary between Bắc Giang and Hải Dương. After flowing through the area of Hải Dương, it enters Thái Bình Province and flows to the South China Sea at Ba Lat river mouth.
The Battle of Như Nguyệt River, also called the Battle of the Cầu River, took place during the final phase of the Song–Vietnamese Border War (1075–1077). The battle occurred along parts of the Cầu River that flows through what later became Bắc Ninh Province of Hanoi in February 1077. At the battle, the Vietnamese led by admiral-general Lý Thường Kiệt stopped the Chinese attempt to cross the river but failed to dislodge them from their position, resulting in a stalemate at the river before the Song retreated due to mounting casualties. The war ended with a peace negotiation.