[@Divine Darkness] Now I had something for Atlantis somewhere in my notes, but I can't find them now. The jist is that before the Drench - the Atlantean's name for the great tragedy that befell them that ended in the sinking of their homes - there was seven kingdoms of Atlantis. In a last ditch to save their people the Mage-Lords of old used the Zodiac stones, seven crystals of immense mystical power, to cast a great spell to stop the Drench. They succeeded, after a fashion, for instead of stopping the sinking of Atlantis as they intended they instead managed to morph their people in to the aquatic bipeds we now know. One Zodiac stone went to each Kingdom, though three of the cities have since been lost to knowledge. 

The Kingdoms that still exist that I can remember off hand are Poseidonis(Aquaman's home), Xebel, Tritonis and Thierna Na Oge. 

So yeah, do that with Xebel. They could have got their reputation for being a penal colony because after they lost Poseidonis labeled them as thieves and cowards.