The Megarian Decree was a set of economic sanctions levied upon Megara c. 432 BC by the Athenian Empire shortly before the outbreak of the Peloponnesian War. This move is considered one of the first uses of economics as a foreign policy tool. The decree addressed the Megarians' supposed trespass on land sacred to Demeter known as the Hiera Orgas, the killing of the Athenian herald who was sent to their city to reproach them, and giving shelter to slaves who had fled from Athens. The Megarian decree effectively blocked Megara from trading in any port within the Delian League, isolating the city and greatly damaging its economy. The exact influence the Megarian Decree had on the beginning of the Peloponnesian War is a matter that is highly debated to this day. Background The Megarian Decree was seen as an act of revenge by the Athenians for the treacherous behaviour of the Megarians some years earlier. It may also have been a deliberate provocation towards Sparta on the part of Pericles, who was the sponsor of the decree. Aristophanes also cited that it was enacted to avenge the theft of the female attendants of Aspasia, who was Pericles' partner. There are scholars who view the Megarian Decree as one of the main causes of the Peloponnesian War. The economic blockade banned Megarians from harbours and marketplaces throughout the large Athenian Empire, which effectively strangled the Megarian economy. The sanctions would have also affected Megara's allies and may have been seen as a move by Athens to weaken its rivals and to extend its influence. Megara controlled the important routes between Peloponnese and Attica, making it crucial for both Athens and Sparta. The ban strained the fragile peace between the two states. The Peloponnesian War began after Megara appealed to Sparta, its ally, for help. In the build-up to the conflict, the repeal of the decree was Sparta's main demand to the Athenians. Thucydides mentions that the revoking of the Megarian decree was only one of several demands made by the Spartans if Athens wished to avoid war, other demands included: an end to the siege of Potidaea, the immediate independence of Aegina, and that the Athenians will not infringe on the independence of the Hellenes. Significance The extent to which the decree encouraged the outbreak of the Peloponnesian War is the subject of debate. The primary source for the war,