Attica is located in what is today southern Greece, and covers about 3,800 square kilometers. In addition to Athens, it contains within its area the cities of Peiraeus, Eleusis, Megara, Laurium, and Marathon, as well as a small part of the Peloponnese peninsula and the islands of Salamis, Aegina, Poros, Hydra, Spetses, Kythira, and Antikythera. About 3,750,000 people live in the periphery, of which more than 95% are inhabitants of the Athens metropolitan area.
Athens was originally the capital of Central Greece.
Attica is a peninsula jutting into the Aegean Sea. Mountains divide the peninsula into the plains of Pedia, Mesogeia, and Thriasia. The mountains include Hymettus, the eastern portion of Geraneia, Parnitha, Aigaleo and the Penteli mountains. To the north it is bordered by the Boeotian plain and to the west it is bordered by Corinth. The Saronic Gulf lies to the south and the island of Euboea lies off the north coast. Athens' first and only large reservoir, Lake Marathon, is about 42 km northeast and is called the Marathon Dam, which first opened in the 1920s. Since that time, it has been Attica's largest lake. Forests cover the area around Parnitha, around Hymettus and into the northeast and the north in the hills and the mountains, except for the mountaintops, but the mountains to the west and the south are grassy, barren or forested.
The Cephisus River is the longest river, and Parnetha or Parnitha is the tallest mountain in Attica. The prefecture also has parklands in the Hymettus, Penteli and the Parnitha mountains and the southern part of the peninsula.
According to Plato, Attica's ancient boundaries were fixed by the Isthmus, and that in the direction of the continent they extended as far as the heights of Cithaeron and Parnes. The boundary line came down in the direction of the sea, having the district of Oropus on the right, and with the river Asopus as the limit on the left.