Agrippa is summoned back to Rome by Octavian to assume the consulship for 37 BCE.
He is well below the usual minimum age of 43, but Octavian has suffered a humiliating naval defeat against Sextus Pompey and needs his friend to oversee the preparations for further warfare.
Agrippa refuses the offer of a triumph for his exploits in Gaul – on the grounds, says Dio, that he thought it improper to celebrate during a time of trouble for Octavian.
Since Sextus has command of the sea on the coasts of Italy, Agrippa's first care is to provide a safe harbor for his ships.
He accomplishes this by cutting through the strips of land which separate the Lacus Lucrinus from the sea, thus forming an outer harbor, while joining the lake Avernu—a crater lake about eight miles (thirteen kilometers) west of Naples and about two miles (more than three kilometers) in circumference and one hundred and eighteen feet (thirty-six meters) deep—to the Lucrinus to serve as an inner harbor.
The new harbor-complex, named Portus Julius in Octavian's honor, is used to train the ships for naval battles.
A new fleet is built, with twenty thousand oarsmen gathered by freeing slaves.
The new ships are built much larger in order to carry many more naval infantry units, which are being trained at the same time.
Furthermore, Antony exchanges twenty thousand infantry for his Parthian campaign with one hundred and twenty ships, under the command of Titus Statilius Taurus.
A tunnel, the Grotta della Sibill, connects the new harbor to …
