The thesis tries to enlighten the period of the third century in the territory between the Northern Adriatic and Southeastern Alps as fully as possible. The thesis is basically divided into two parts. The theoretical descriptive part presents previous researches, discusses ancient literary sources and outlines military, political, administrative and economic history. The second part of this text is an archaeological image examining individual phenomena that are typical for the third century in Slovenia. The end of the thesis is an attempt of collecting all the sites in Slovenia that were active in the discussed period.