The teenage boys who demonstrated the most leadership potential were selected for participation in the Crypteia, which acted as a secret police force whose primary goal was to terrorize the general Helot population and murder those who were troublemakers. At age 20, Spartan males became full-time soldiers, and remained on active duty until age 60.

The Spartans' constant military drilling and discipline made them skilled at the ancient Greek style of fighting in a phalanx formation. In the phalanx, the army worked as a unit in a close, deep formation, and made coordinated mass maneuvers. No one soldier was considered superior to another. Going into battle, a Spartan soldier, or hoplite, wore a large bronze helmet, breastplate and ankle guards, and carried a round shield made of bronze and wood, a long spear and sword. Spartan warriors were also known for their long hair and red cloaks.