The Peloponnesian War (431–404 BC), waged between Athens and Sparta and their respective allies, involved some of the most important developments in ancient warfare. A life-and-death struggle between the two most powerful Greek city-states in the wake of their combined successes against the Persian invasion of Xerxes in 480–479 BC, the conflict dragged in communities from all over the Greek world on one side or the other. Ranging from the Black Sea to Sicily, the war saw the first recorded widespread use of light-armed troops, reserves, the deep phalanx, and other ideas important for the development of Western warfare into the 4th century BC, such as strategic thinking. It also revealed lessons (some learned and some not) with respect to the strengths and weaknesses of hoplite warfare and the various states in Greece. Featuring full-color artwork and drawing upon an array of sources, this study of three pivotal clashes between Spartan and Athenian hoplite forces during the Peloponnesian War highlights all of these developments and lessons.