Sparta was the most powerful city-state in ancient Greece for nearly three centuries. Located in the Southern area known as Pelloponnese, Sparta became the dominant force of the allied Greek armies during the Greco-Persian wars. Sparta and Athens were enemies during the Pelloponnesian War between 431-404 B.C. Sparta's decline began when they were defeated by Thebes in 371 B.C. and later by the Macedonians. The Spartans were arguably the most militaristic group in ancient history. Children deemed too weak after childbirth were often killed, and most of the males began their military training at the age of seven. Spartans became reserve members of the military at age 18 and were expected to serve until the age of 60. They were deliberately given only enough food to subsist, and their luxuries were few: thus, the term a "Spartan existence." Their military numbers varied from battle to battle. At their defeat to the Thebans at the Battle of Leuctra, the Spartan army numbered about 12,000. Children did receive an education beyond the military; reading, writing, music and the arts were studied. Spartan females also received an education--a rarity in ancient Greece.