Julius Caesar described the Gallic Wars in his book "Commentarii de Bello Gallico". This is the main source, but it makes impossible claims about the number of Gauls killed (over a million), while claiming few Roman casualties. Modern historians believe that Gallic forces were far smaller than Caesar claimed, and that they (the Romans) suffered tens of thousands of casualties. One of the leaders of the Gauls, Vercingetorix, was taken to Rome, and later executed.