Lycastus was a demigod and a son of Ares, the god of war.
Lycastus, twin brother of Parrhasius, whose parents were Ares and Phylonome, daughter of Nyctimus and Arcadia. Their mother was seduced by Ares in the guise of a shepherd; in fear of her father's wrath, she cast the newborn twins into the river Erymanthus. They did not drown and were washed into the hollow of an oak tree, where a she-wolf found and suckled them, giving up her own cubs.
The twins were then adopted and raised by a shepherd named Glyphius, and eventually succeeded to the throne of Arcadia. Their story is closely parallel, and is cited as such by Pseudo-Plutarch, to that of Romulus and Remus.