Zeus was his immortal father .
The god had to assume a stallion 's form to cover Dia for , like their half - horse cousins , the Lapiths were horsemen in the grasslands of Thessaly , famous for its horses .
Zeus was his immortal father , but the god had to assume a stallion 's form to cover Dia for , like their half - horse cousins , the Lapiths were horsemen in the grasslands of Thessaly , famous for its horses .