This article is about a Greek military alliance. For the federation of communities into a
polis, see
Synoecism. For the confederation of multiple independent communities in a single politeia, see
sympoliteia. For the municipal unit in modern Greece, see
Sympoliteia (municipality). For the genus of butterflies, see
Symmachia.
A symmachia (Greek: συμμαχία, romanized: symmachia) is and was in ancient times a military treaty between independent polities covering both offense and defense. In modern Greek the word also can mean an alliance among political factions to form a political party.