The question of who attended the regular assemblies (synodoi) of the Achaian koinon in the 2nd century BCE is still a subject of discussion. Two main theories prevail: the synodos either was a primary assembly of all citizens or a meeting of the federal council. However, the very existence of an elected council in the koinon can be doubted, since no trace of activity of this federal body in the 3rd and the 2nd centuries BCE can be found, either in literary, or epigraphic sources. The only evidence supposedly proving the existence of an Achaian council is the frequent mention of the word boule in Polybios’ accounts of the federal assembly meetings. Attentive consideration of these passages leads to the conclusion that, in the lexicon of the Achaian historian, boule is not the official name of a state institution and does not necessarily mean “a council.”
Of the two theories, seeing the synodos as a meeting of the primary assembly seems to be the most compatible with the evidence. However, in light of the recently found inscription SEG LVIII 370, we may be certain that in Polybios’ time the synodos was a representative body – and therefore not a people’s assembly in the strict sense of the word. The only reasonable interpretation of this contradictory evidence appears to be the following: the synodos was a meeting of several thousand delegates representing all the Achaian poleis, the size of each delegation being determined in proportion to the population of the community. The list of these delegates varied from meeting to meeting, and therefore the synodos should not be regarded as a body with permanent membership, such as a state council. This kind of assembly also might have served as a model for the archairesiake ekklesia of the Lykians.