Krypteia

The secret service, or the secret thing. Plutarch describes young Spartans sent out into the countryside with daggers and rations, hiding by day and killing helots on the roads at night, taking the strongest first.

He attributes the account to Aristotle, and is careful to add that Aristotle also recorded the ephors declaring war on the helots on entering office each year, so that killing one incurred no religious pollution. Plutarch himself doubts the institution goes back to Lycurgus, and says so.

The evidence is thinner than the reputation. Plato refers to the krypteia as a form of endurance training, hard living outdoors through winter, with no killing mentioned. Whether it was a death squad, a survival ordeal, or something that changed over three centuries, the surviving sources do not settle.