a joining together of several towns to form a single community, as in ancient Greece. — synoecy, n. — synoecious, adj.
This was done in Ancient Greece where Athens proper was unified with the country towns and villages of Attica under one government. The festival of Synoecia is a celebration of the political union of Athens and Attica, but is distinctly separate from Panathanaia which is the religious festival - held next Sunday. I wont go into Synoecia as it is more of a secular, national holiday like Waitangi Day or Queen's Birthday.