Noun
dodecapolis (plural dodecapolises or dodecapoli)
A group or confederation of twelve cities.
Etruscan League According to legend, there was a period between 600 BC and 500 BC in which an alliance was formed among twelve Etruscan settlements, known today as the Etruscan League, Etruscan Federation, or Dodecapolis (in Greek Δωδεκάπολις). Source: Internet