The article is devoted to the methods of classification of ancient toponyms from the point of view of their external and internal structure. The first paragraph of the article gives a brief outline of the history of the issue. Despite the generally large number of works devoted to individual problems of ancient Greek toponymy or individual toponyms, only a few works in both domestic and foreign scientific historiography are devoted to the study of ancient Greek toponymy as a system from a philological point of view. The object of research in this article is the problems of creating a common word-formation-semantic classification of ancient Greek geographical names as a whole. The subject of the study is the ancient toponyms of the Cilician plain (Greek. Κιλικία πεδιάς) – low plains in the south of modern Turkey. Among the toponyms of Plain Cilicia, geographical names of ancient Greek and Latin origin (24 ancient Greek and 5 Latin names) were selected and analyzed for morphological structure and semantic features. Special attention is paid to the problems of etymologization of toponyms and the indication of centuries of fixation. The classification of ancient Greek toponyms, proposed in a 1965 article by the Swiss Hellenist Ernst Risch, is taken as a basis. The results of the study are presented in a table reflecting the four main word-formation types of ancient Greek toponyms in diachrony.