crater lake in Napoli province, Campania region, southern Italy, in the Campi Flegrei volcanic region, west of Naples. It is 7 ft (2 m) above sea level, 118 ft deep, and nearly 2 mi (more than 3 km) in circumference, with no natural outlet. Its Greek name, Aornos, was interpreted as meaning “without birds,” giving rise to the legend that no bird could fly across it and live because of its poisonous sulfurous vapours. Surrounded by dense forests in ancient times, it was represented by the poet Virgil as the entrance to Hades (hell). The Carthaginian general Hannibal made a pilgrimage to it in 214 BC. Agrippa, the Roman statesman, in 37 BC cut down the forest (now replaced by vineyards) and converted the lake into a naval harbour, the Portus Iulius, which was linked to the sea by a canal via the Lago di Lucrino and to Cumae by a tunnel more than ¹/₂ mi long, the world's first major road tunnel. The canal was soon blocked because of a gradual rise of the shore, but the tunnel, now called the Grotta di Cocceio (or della Pace), remained usable until it was damaged during World War II. The so-called Grotta (or pseudo-Grotta) della Sibilla is a rock-cut passage, possibly part of the works connected with the naval harbour. Impressive Roman ruins include the remains of baths, temples, and villas.