The article assesses the degree of similarity between regional sets of motifs in the southwestern half of Eurasia with each other and with motifs from ancient (mostly Greek) sources. The analysis includes adventure episodes, narrative clichés and fantastic images found in mythological prose, heroic epics and fairy tales. In the Balkans, almost all motifs from ancient sources have correspondences in late folklore, but ancient correspondences make up less than a fifth of the total number of Western Eurasian motifs in the categories of tales under consideration. The rest are likely borrowings from Central Asia, the Near East — Iran — India and motifs that arose in Europe itself. The role of early traditions not reflected in written sources and located to the north of the Aegean is debatable. Slavic traditions of Eastern Europe are much closer to Western European ones than to Turkic-Mongol traditions. The process of enrichment of Western Eurasian folklore took place as population density increased, contacts between groups intensified, and genres of folklore emerged that had lost their connection with a specific ethnic basis and their focus on authenticity. In terms of the number of registered motifs, the traditions localized from the Aegean to the Eastern Baltic represent the world maximum.