One of eight regional units formed within the Attica Administrative Region, which was previously known as the Attica Prefecture (Νομὸς Ἀττικῆς) until abolished in 2011 per the 2011 "Kallikratis" agreement. The "Kallikratis" program decentralized the entirety of Greece, breaking apart the former prefectures into units, and reducing the number of municipalities from 1034 to 325. The Piraeus regional unit covers the eastern part of Athens Urban Area, aka the Urban Area of the Capital (Πολεοδομικό Συγκρότημα Πρωτεύουσας), and was once known as the Piraeus Prefecture, which was also abolished in 2011.
