Excerpts from Books and Wikipedia
Two million Germanic Visigoths and Ostrogoths crossed into the empire west of the Black Sea in 376. In 378, the barbarian warriors camped 12 miles (20 km) outside of Adrianople. Valens was the ruler of the eastern half of the Roman Empire. He marched his army from Constantinople and attacked the barbarians without waiting for the arrival of Gratian, the Western Roman Emperor. Two-thirds of the Roman soldiers (40,000 men) were killed. The body of Valens was never found. [Furtado: 1001 Days]