The Peloponnesian Peninsula, also called simply the Peloponnesus, is a mountainous landmass connected to Attica, easternmost province of Central Greece, by an isthmus only six kilometers wide at its narrowest point. The isthmus is cut by the Corinth Canal, which allows marine traffic to move between the Aegean and the Ionian seas north of the Peloponnesus via the gulfs of Corinth and Patras. The canal, originally planned by the Roman emperor Nero in the first century A.D. and completed in 1893, shortens this voyage by 325 kilometers.
The Pindus Range continues southward from the mainland across the peninsula, extending into each of the three peninsulas that are the southernmost points of the Peloponnesus. Between the mountains is the Plateau of Arcadia (Arkadia). Lowlands extend along the western and northern coasts, along inland river valleys, and in spring-fed mountain basins. Alluvial plains in the east and south are fertile, but agriculture requires irrigation. Most of the peninsula's rivers are dry in summer.
All the population centers of the Peloponnesus, except for Tripolis in the mountains, are on the periphery of the peninsula. Sparta, once the most powerful polis in Greece, is several kilometers inland on the plain of the Evrotas River. Corinth, another major polis of classical times (and the origin of the word currant because of its role in exporting that crop), is now a relatively unimportant small city on the northeast coast. The largest city is Patras (Patrai), an important industrial, commercial, and port city on the northern coast. The other major port is Kalamai in the southwest.
Peloponnesus is politically divided into seven prefectures: