Eridanos was the small stream that flowed from a source in the foothills of the Lykabettos, through the Agora

Agora

The Agora was an open "place of assembly" in ancient Greek city-states. Early in Greek history , free-born male land-owners who were citizens would gather in the Agora for military duty or to hear statements of the ruling king or council. Later, the Agora also served as a marketplace where...

 of ancient Athens in Greece

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 to the archaeological site of the Kerameikos, where its bed is still visible. In this area lives a population of Greek Tortoise

Greek Tortoise

The spur-thighed tortoise or Greek tortoise is one of four European members of the Testudinidae family of tortoises...

.
Its course has been for the most part covered since ancient times, and was only visible outside the ancient walls in the district of Kerameikos http://www.culture.gr/2/20/201/2011/201101/e201101c.html#5.

The river was rediscovered during the excavations for the Athens Metro

Athens Metro

The Athens Metro is an underground rapid transit system serving Athens, the capital city of Greece. It was constructed and owned by Attiko Metro S.A. and operated until 2011 by Attiko Metro Etaireia Leitourgias S.A....

 subway in the late 1990s, and its waters caused considerable technical problems at times. Because of the Metro works, its seasonal flow through the Kerameikos cemetery was disrupted, as the waters were apparently and inadvertently redirected to some new underground path.

As of April 2007, the stream of the river, as it flows through Monastiraki

Monastiraki

Monastiraki is a flea market neighborhood in the old town of Athens, Greece, and is one of the principal shopping districts in Athens. The area is home to clothing boutiques, souvenir shops, and specialty stores, and is a major tourist attraction in Athens and Attica for bargain shopping...

 Square, has been excavated. It had been covered with a brickwork tunnel since classical times, and the brickwork had been repaired at least twice, in the imperial Roman

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 and early Byzantine

Byzantine

Byzantine usually refers to the Roman Empire during the Middle Ages.Byzantine may also refer to:* A citizen of the Byzantine Empire, or native Greek during the Middle Ages...

 eras. The brick tunnel now forms part of a small open-air museum at Monastiraki Square, next to the Metro station

Monastiraki station

This page addresses a train station in Greece; for the ancient Cretan city, see Monastiraki, Crete.Monastiraki or Monastirion station is an interchange station of the Attiko Metro Blue Line and the ISAP Green Line 1. The original surface station of Line 1 opened in May 17, 1895...

, and the waters of the Eridanos are audible from inside the tunnel.