In 214 BC, the Qin dynasty undertook a military campaign against the southern Baiyue tribes to conquer the territories of what is now southern China and northern Vietnam.
In 214 BC, the First Emperor secured his boundaries to the north with a fraction (300,000 men) of his large army, and sent the majority (500,000 men) south to seize still more land. At that time southern China is known for its fertile land, elephant tusks and jade production. Prior to the events leading to Qin dominance over China, they had gained possession of much of Sichuan to the southwest. The Qin army was unfamiliar with the jungle terrain, and was defeated by the southern tribes' guerrilla warfare tactics with over 100,000 men lost. However in the defeat Qin was successful in building a canal to the south, which they used heavily for supplying and reinforcing their troops during their second attack to the south. Building on these gains, the Qin armies conquered the coastal lands surrounding Guangzhou and took areas of Fuzhou and Guilin. After these victories in the south, the First Emperor moved over 100,000 prisoners and exiles to the newly conquered area to colonize them. By 208, Zhao Tuo had reached Co Loa, the capital of the Vietnamese state of Au Lac, 16 km (10 mi) northeast of present-day central Hanoi.