Erymanthus (all: ĕr'ĭmăn`thəs), mountain group, S Greece, in NW Peloponnesus, on the border of Achaea, Arcadia, and Elis. The highest peak (c.7,295 ft/2,220 m) is Mt. Erymanthos, also known as Mt. Olonos. In mythology the mountains were the haunt of the Erymanthian boar that Hercules captured.