" Nico had once read a story from Plato, who claimed that in the ancient times, all humans had been a combination of male and female. Each person had two heads, four arms, four legs. Supposedly, these combo-humans had been so powerful they made the gods uneasy, so Zeus split them in half—man and woman. Ever since, humans had felt incomplete. They spent their lives searching for their other halves. "

― Rick Riordan , The Blood of Olympus (The Heroes of Olympus, #5)