The harbour

Livius mentions an early Volscian settlement in the area called Caenon, in 469 BC. Presumably it had a harbour, perhaps in modern Nettuno, a bit to the east of Antium:

Melius in Volscis imperatum est; fusi primo proelio hostes fugaque in urbem Antium, ut tum res erant, opulentissimam acti. Quam consul oppugnare non ausus Caenonem, aliud oppidum nequaquam tam opulentum, ab Antiatibus cepit.	The Volscian expedition was better directed: the enemy were routed in the first engagement and driven in flight to Antium, a very opulent city for those days. This place the consul did not venture to assail, but he captured from the Antiates another town, named Caeno, of far less wealth.
Livius, Ab Urbe Condita II,63,6. Translation B.O. Foster.

Antium is situated on a bay, but did not have a natural harbour, as noted by Strabo in the early first century AD:

Such, then, is this city of Ostia. Next comes Antium, it also being a harbourless city. It is situated on masses of rock, and is about two hundred and sixty stadia distant from Ostia. Now at the present time Antium is given over to the rulers for their leisure and relief from the cares of state whenever they get the opportunity, and therefore, for the purposes of such sojourns, many very costly residences have been built in the city; but in earlier times the people of Antium used to possess ships and to take part with the Tyrrheni in their acts of piracy, although at that time they were already subjects of the Romans.

Strabo, Geography V,3,5. Translation H.L. Jones.

A new harbour was constructed by Nero:

Antium coloniam deduxit ascriptis veteranis e praetorio additisque per domicilii translationem ditissimis primipilarium; ubi et portum operis sumptuosissimi fecit.	He established a colony at Antium, enrolling the veterans of the praetorian guard and joining with them the wealthiest of the chief centurions, whom he compelled to change their residence; and he also made a harbour there at great expense.
Suetonius, Nero 9. Translation J. C. Rolfe. See also Tacitus, Annals 14,27.

This ancient harbour had two basins. The northern part of the basins is today a built-up area. One basin conincides with the present-day harbour, which was built by pope Innocentius XII at the end of the 17th century. The other basin was directly to the west. Remains of piers-jetties, for protection and for mooring, have been identified above water and underwater, together with columns and parts of collapsed buildings that stood on top. The piers-jetties were solid, they did not have arches. Noteworthy is an internal narrow pier-jetty in the western basin, for extra protection, or perhaps a reserved mooring space.

Aerial photo of the western ancient harbour. Photo: Felici 2002, Fig. 27.

Plan with the remains of the piers-jetties of the ancient harbour.
a: "Panfili" pier; b: remains below villa Sarsina; c: remains of the western pier; d: remains of the eastern pier; e: collapsed brick walls;
f: submerged remains of the western pier; g: unidentified structures; h: remains of the internal pier-jetty. Image: Felici 2002, Fig. 6.

Suggested piers-jetties of the ancient harbour. Photo: Felici 2002, Fig. 29.

Remains of the western pier. Photo: Wikimedia, Luciano Tronati.

An inscription found near the eastern basin records the restoration of baths that were in danger of collapsing by Anicius Auchenius Bassus in the years 379-382 AD, during the reign of Gratianus, Valentinianus and Theodosius (EDR171326). The harbour is mentioned for the last time in 537 AD: "ships anchored at Anthium, a day's journey distant from Ostia" (Procopius, Gothic War V,26,17).

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