Caesar was the commander of the Roman legions during the Gallic War. The war was fought on the side of Rome's Gallic clients against the Germans, who wanted to invade Gaul. It was also to extend Rome's control of Gaul. Caesar's conquest of Gaul extended Rome's territory to the North Sea. In 55 BC he conducted the first Roman invasion of Britain. Caesar wrote about this eight-year war in his book "De Bello Gallico" ('About the Gallic Wars'). This book, written in Latin, is an important historical account.