Althaemenes or Althemenes (Gr. Template:Polytonic or Template:Polytonic) was in Greek mythology a son of Catreus, the king of Crete. He was also the brother of Apemosyne, Aerope and Clymene. An oracle told Catreus that he would be murdered by one of his children. Althaemenes took Apemosyne and left Crete for Rhodes, where they landed at a place which he called Cretenia, and in remembrance of the god of his own native island, he erected on Mount Atabyrus (modern Mount Attavyros in Attavyros) an altar to Zeus Atabyrius.
It was in Rhodes that Apemosyne was raped by the Greek god Hermes, who had captured her by skinning animals and leaving their slippery hides in her path. When she told Althaemenes, he disbelieved her story and kicked her so hard that she died. Years later, Catreus sailed the seas searching for his son, the heir to the throne. In the middle of the night, his ship stopped at Rhodes and was mistaken for a pirate ship. Althaemenes and others attacked the 'invaders', and the prophecy came to pass; Catreus died at the hands of his son, from a javelin blow. When the boy discovered the truth, he prayed that the earth would open up and swallow him, which it did.
This is the story as related in the Bibliotheca of Pseudo-Apollodorus. The writer Diodorus Siculus agrees in most of the particulars, except he describes Althaemenes as not being swallowed by the Earth, instead wandering about after the murder, eventually dying of grief. He adds that the Rhodians subsequently worshiped him as a hero.