The subject of this paper is the evolution and nature of decimation, a typical capital punishment in Roman military system. Decimation is a ‘collective’ penalty, because it expresses the solidarity that binds together as one all members of the military unit which is guilty of cowardice or desertion. Since such conducts are in themselves detrimental to the oath sworn by each soldier to his military commander and to his comrades, it can be assumed that the death penalty (collective or individual) that applies in such cases is to be placed in the area of punishments with a ‘sacral’ character, and therefore does not allow the offender access to the provocatio ad populum.