Grotta di Cocceio, also known as the Cocceius Tunnel, is a straight-line subterranean gallery nearly a kilometre in length connecting Lake Avernus with Cumae north of Naples, Italy. It was burrowed clean through the tuff stone of Monte Grillo from 38-36 BC. The tunnel was effected by the architect Lucius Cocceius Auctus at the wishes of Agrippa who was in the process of converting the Lake into a military port, the Portus Julius. The Avernus side of the passage was decorated with a colonnade and had many statues in niches hewn into the tufa stone walls of the entrance.
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