The Peloponnesian War (431–404 BC) was fought between two of the most powerful ancient Greek city-states, Athens and Sparta. In the summer of 424 BC, its contemporary historian, the Athenian Thucydides, recorded an Athenian assault on the town of Megara, a Spartan ally. It would have succeeded had not the Spartan general Brasidas arrived. He was not allowed into the city, however, because ‘the Megarians were watching to see which side would win’. After some cavalry skirmishing, the two armies drew up for battle. Brasidas, on favourable ground, ‘did not have to run any risks … and might [have won] an unopposed victory’. But neither side engaged. After a while the Athenians retreated, deciding that they ‘had achieved most of their objectives and did not want to run the risk of losing some of their best hoplites’, and Brasidas was at last welcomed into Megara.