Summary. This article seeks to analyse the reform of the conscription that took place in Peru at the beginning of the twentieth century with the application of the Military Service Act of 1898. Our proposal is that while the application of the law changed the old decimonic practices of compulsive or negotiated constitution of the limestone armies, it could not be fully complied with due to the administrative and coercive constraints of the state and the resistance of various social groups. Nevertheless, the rule allowed large military units to be set up in a bureaucratic and centralised manner.