The Asopos (Greek: Ασωπός, referred to in Latin sources as Asopus) is a river in Boeotia and northern Attica, Greece. In antiquity, it formed the border between the cities of Thebes and Plataea. The Battle of Plataea was fought on its banks. According to Pausanias (5.14.3) the Boeotian Asopus can produce the tallest reeds of any river.
Its source is on the northern slope of the Cithaeron mountain, southwest of Thebes. It empties into the South Euboean Gulf, near Skala Oropou. Its total length is 57 km. Its basin is 718 km2. The Asopos flows along the following places, from the source downstream: Lefktra, Agios Thomas, Oinofyta, Sykamino, Skala Oropou. The river is polluted with hexavalent chromium due to industrial activity.
Pausanias (9.1.1) cites Plataean tradition that Asopus was ancient king of that region in succession to King Cithaeron who gave his name to the mountain as King Asopus gave his name to the river and that the city Plataea was named after Plataea daughter of the river Asopus. Pausanias then comments oddly that he thinks that this eponymous Plataea was daughter of King Asopus rather than of the river Asopus.
Boeotia, sometimes alternatively Latinised as Beotia (/biːˈoʊʃiə/ or /biːˈoʊʃə/; Greek: Βοιωτία, Modern Greek: [vi.oˈti.a], Ancient Greek: [bojɔːtía]; modern transliteration Voiotía, also Viotía, formerly Cadmeis), is one of the regional units of Greece. It is part of the region of Central Greece. It was also a region of ancient Greece. Its capital is Livadeia, and its largest city is Thebes.
Boeotia lies to the north of the eastern part of the Gulf of Corinth. It also has a short coastline on the Gulf of Euboea. It bordered on Megaris (now West Attica) in the south, Attica in the southeast, Euboea in the northeast, Opuntian Locris (now part of Phthiotis) in the north and Phocis in the west.
The main mountain ranges of Boeotia are Mount Parnassus in the west, Mount Helicon in the southwest, Cithaeron in the south and Parnitha in the east. Its longest river, the Cephissus, flows in the central part, where most of the low-lying areas of Boeotia are found.
Lake Copais was a large lake in the center of Boeotia. It was drained in the 19th century. Lake Yliki is a large lake near Thebes.