Portus Julius was commissioned by Marcus Vipsanius Agrippa during the civil war between Octavian and Sextus Pompey (37 BC). The magnificent port was intended for the impressive arsenal of the Classis Misenensis, the most important Roman fleet. It’s construction was entrusted to the architect Lucius Cocceius Auctus, whose ingenuity ensured the port’s connection to Lake Lucrine and Lake Avernus via a navigable canal and to Cumae by a 1 km (0.6 mile) long underground tunnel through which chariets could pass. Ultimately, the naming of the port itself was in honour of Gaius Julius Caesar Augustus.

Once complete, Portus Julius offered a comprehensive array of administrative naval services: warehouses for the storage of food and supplies, cisterns for potable water, dry docks for hull maintenance and workshops for the repairing of sails. Other, more personal needs were equally provided for: recreational facilities, the Temple of Poseidon, and discreet brothels.

However, the military life of the port was short on account of silting. As early as 12 BC the imperial fleet was moved to the nearby natural pools of Miseno and the port was reverted to civilian purposes. It was from this location that galleys were dispatched on the orders of Naval commander Gaius Plinius Secundus to evacuate the horror-striken inhabitants of Pompeii and Herculaneum during the catastrophic eruption of Mount Vesuvius in 79 AD.

With the passing of millennia, the original complex has been fated by bradyseism (caused by volume changes in an underlying magma chamber and/or hydrothermal activity). In the late fifth centuary Flavius Magnus Aurelius Cassiodorus Senator noted that the outer breakwater of the port had fallen into disrepair; in the following centuaries it disappeared completely, reuniting Lucrino with the sea. This lateral movement of the coast continued until 29 Septmber 1538 when an eruption occurred generating the so-called New Mountain, distroying the village Tripergola and reducing Lake Lucrino to little more than a pond.

Portus Julius again came to light via aerial photography taken during World War II. Pictures taken illustrate the topography of the extensive portal complex which covers an area of approximately 10 hectares. Buildings used as warehouses could be identified along with various column arrangements denoting courtyards of residential houses. Indeed, most of the mapping of the area has been compiled from studying such photographs.

The details pertaining to the port’s construction have, however, been obtained via underwater surveys and observations. The walls and pillars rise from a few inches to more than a meter above the sea-bed and their stonework bears witness to the various building methods used, particularly reticulated work. Pathways, floor mosaics, ceramic wares and even the indication of frescoes can still be found in-situ.