Never before the nineteenth century had Europeans, especially in the south, adopted cordons sanitaires in such great numbers or at such a fast rate. This article aims to analyse the process of the rationalisation and militarisation of the cordons sanitaires imposed in the fight against epidemics during the nineteenth century on the Mediterranean island of Majorca (Spain). These cordons should be understood as a declaration of war by the authorities on emerging epidemics. Epidemics could generate sudden and intolerably high rises in mortality that the new liberal citizenship found unacceptable. Toleration of this type of measure was the result of a general consensus, with hardly any opposition, which not only obtained the support of scientists (especially in the field of medicine) but also of most of the local and provincial political elite, and even of the population at large.