This article deals with the motivation for the persecution of Christians during the Roman tetrarchy of 303-311/313. In the first part, five main explanations are presented, which can be found both in the sources itself and in modern research. As none of these explanations can claim an absolute interpretation, there is room for another theory. In the second part, I try to prove that theory: I act on the assumption, that the Christians didn't provoke the persecution by their behaviour, but were chosen as a group of victims because they were “different”. The exclusion, resulting of that persecution, should starch the identity of the other inhabitants of the empire. This was possibly to balance the threatening deficit of stability after the intended abdication of Diocletian in 305. In fact there are evidences for this theory in the sources: Mainly the exotification of the Christians demonstrated by the concrete measures of the persecution as described by Eusebius are an evidence, that the persecution of Christians during the tetrarchy was motivated to consolidate the stability in the empire by using the simple sociological mechanism of “Identity per Exclusion”.