"Once upon a time, they say, a serpent lived in the sky and flew throughout the world; everyone feared him, and some even worshiped him. When God learned of his worship, he took his wings, and he fell from the sky into the Dnieper and swam away. The idol worshipers fled along the shore, shouting, 'Perun, Perun, come to shore.' He swam to an island, and a deep hole opened up for him; he disappeared there. From that time on, the island was called Perun."
The problem of correlating the images of Perun and the Serpent requires separate consideration (for example). For skeptics, we present several more illustrative testimonies about Perun's serpentine nature. A Slavic insertion in "The Conversation of St. Gregory the Theologian on the Slaughter of the City" (11th century):
"<...>He calls the river a goddess and performs sacrifices to the beast living in it, calling it a god. One worships Dyya, and the other Divia."
Divia is clearly associated with the river goddess, and Dyy with the "beast" living in the river. Zeus, under the name Dyy (Diy), is known to Russian scribes from the translation of Hamartolus, as demonstrated by