1) Ancient Greek geography 
[Attica] Tetrapolis (Greek: Τετράπολις) comprised one of the twelve districts into which Attica was divided before the time of Theseus. The district was on a plain in the northeastern part of Attica and contained four cities: Marathon (Μαραθών), Probalinthus (Προβάλινθος), Tricorythus (Τρικόρυθος), and ...
group of four cities
(from the article `ancient Greek civilization`) ...site in Classical and Hellenistic times, seems to have been anomalously attributed to a city trittys; and an ancient local organization known as ...
tetrapolis A district of four cities; a state or political division consisting of four towns.