Types of eugenic practices have existed for millennia. Some indigenous peoples of Brazil are known to have practiced infanticide against children born with physical abnormalities since precolonial times. In ancient Greece, the philosopher Plato suggested selective mating to produce a guardian class. In Sparta, every Spartan child was inspected by the council of elders, the Gerousia, which determined if the child was fit to live or not. In the early years of the Roman Republic, a Roman father was obliged by law to immediately kill his child if they were "dreadfully deformed". According to Tacitus, a Roman of the Imperial Period, the Germanic tribes of his day killed any member of their community they deemed cowardly, unwarlike or "stained with abominable vices", usually by drowning them in swamps. Modern historians, however, see Tacitus' ethnographic writing as unreliable in such details.