To the north of the Arimaspi were the Rhipean Mountains and a region called Pterophorus because of the feather-like snow, which continuously fell there. This is in all probability a reference to Herodotus’ feathers which the Scythians say fill the air and make it impossible to traverse, or even to see, the more northerly part of the continent (Herodotus 4.31). These feathers may be a reference to the swan which Apollo rode or to the swans which pulled Apollo’s chariot to the land of the Hyperboreans in Alcaeus’ text.

Timothy Bridgman, Hyperboreans: Myth and History in Celtic-Hellenic Contacts