With the displacement of the fleet from Portus Iulius to the port of Miseno in 12 BC and the end of the Civil War between Octavian and Mark Antony in 31 BC the tunnel lost its strategic value. The forum entrance was made monumental with 4 statue niches in 95 AD at the same time as the Arco Felice was built. An avalanche closed the sea entrance in the 3rd c. After 397 it was reopened. In the christian age it was used as a cemetery area; in the 6th c. the Byzantine general Narsete tried to use it to reach the city during the siege of Cumae, but weakened the structure and a large section of the vault collapsed.