Etruscan Bronze Mask of Achelous, c. 520 BC

In Greek mythology, Achelous was the patron deity of the “silver-swirling” Achelous River, which is the largest river of Greece, and thus the chief of all river deities, since every river was believed to have its own spirit. His name is pre-Greek, its meaning unknown. In ancient art his image is often reduced to just a bearded mask, and he is believed to be the origin of the medieval Green Man

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