The chief way in which the Greeks united in the third century in order to be able to offer resistance to Macedon was by forming large federal states. The two greatest of these were based in Achaea and in Aetolia, but both quickly spread well beyond these ethnic borders. “Aetolia” came to mean almost all of central Greece, and “Achaea” much of the Peloponnese. I discuss the differences between confederacies and the most familiar form of ancient Greek polity, the polis, and show how confederacies gained their strengths, before focusing on the structures set up by the Aetolians and Achaeans. By the time Antigonus came to the Macedonian throne, the Achaeans were on the rise, but the Aetolians were already a powerful threat. They had spearheaded the Greek repulsion of the Celts from central Greece, thus preserving Delphi, the most important of the Greeks’ common religious centers, and they used this as a springboard for further expansion. Antigonus treated them warily throughout his reign.