Grotta di Cocceio

Grotta di Cocceio is a Roman tunnel cut through the tuff between Cumae and Lake Averno. About a kilometre long, it was designed in 38–36 BCE by Lucius Cocceius Auctus for the harbour complex built by Agrippa for Octavian.

Why it matters

The tunnel is an ambitious work of Republican-era engineering, created to connect Cumae with the concealed naval harbour at Portus Iulius. Its later uses—as part of an aqueduct system, a Bourbon road and a Second World War depot—show how the same passage served changing needs over two millennia.

What to notice

The gallery runs in a straight line through the rock, with a broad, high section suited to wheeled traffic. Nine light shafts pierced the vault to bring daylight and ventilation into the passage. A side branch near Cumae, probably associated with movement toward the amphitheatre, and a connection to a branch of the Serino aqueduct belong to the tunnel's later Roman use.

Context and history

After Octavian's victory at Actium in 31 BCE, the harbour's military purpose ended and the tunnel was adapted for civilian use. It gradually silted up before Bourbon-era excavation returned it to use as a road in 1844. During the Second World War it served as an ammunition depot; an explosion in 1943 damaged the structure. The archaeological park also documents a bat colony in the tunnel and conservation measures intended to protect it.