According to our surviving narratives, the three kings of Rome during the Etruscan occupation were Tarquinius Priscus, Servius Tullius, and Tarquinius Superbus. During this period the army underwent a reformation into a "centurial" army based on socio-economic class. This reformation is traditionally attributed to Servius Tullius, the second of the Etruscan kings. Tullius had earlier carried out the first Roman census of all citizens. Livy tells us that Tullius reformed the army by transplanting onto it the structure derived originally for civil life as a result of this census. At all levels, military service was, at this time, considered to be a civic responsibility and a way of advancing one's status within society.