This article investigates the thoughts of Roman authors about the causes of the civil war (49-45 BC). Caesar, Cicero and Velleius Paterculus consider the passions and the immorality of the persons as the causes of this war. According to Seneca and Lucan, the political ambitions of Caesar, Pompey, their supporters, as well as the passions of the whole society caused the civil war. But Lucan paid attention also to objective conditions.