A cape at Puteoli did not provide enough safety for ships, and a breakwater was deemed necessary. It must have been some 370 meters long and was made up of a series of arches. In the early 20th century fifteen massive piers could still be seen. These then became part of a modern mole. They were described by Giuliano de Fazio in 1828, and Charles Dubois was just in time to inspect the remains, of which he published a description in 1907.

Map from Beloch 1890.

The mole was perpendicular to the coast and slightly curved. The piers measured 16 x 16 m. and were 10 m. apart. The concrete core was faced with large tufa blocks and bricks, belonging to the original building phase and repairs. Some blocks had holes (diam. 0.40) for mooring ships. A lighthouse resting on a mole is not documented for Puteoli.

The remains of the breakwater as seen in the 17th century. Image: BNF.

Reconstruction drawing of the mole. Image: Dubois 1907, fig. 19.

The first certain reference to the mole in ancient literature is a Greek poem by Philippus of Thessalonica, dated to the period of Claudius-Nero. It might be related to the construction.

The barbarian bridged the Hellespont in his daring folly, but Time dissolved all that labour. Now Dicaearchia has made the sea a continent, and given the depths the form of dry land. She fixed firmly in the depths a vast supporting structure of stone, and with the hands of the Giants made the water beneath stand still. We could always sail over the sea, but insecure as it was for sailors who travelled on it, it has now promised to remain secure for foot-travellers.

Anthologia Palatina IX, 708. Translation W.R. Paton.

The area to the north of the breakwater was thus protected. Piers supporting arches have also been seen in the sea to the south-east. At 100 meters from the coast was a double row of alternating piers. The piers of the outer row measured 6 x 8 m. and were 4 m. apart. The piers of the inner row were trapezoidal and somwehat smaller. Between the piers and the coast were continuous walls, creating basins, presumably fish-ponds.

The basins to the south-east of the mole. Image: Dubois 1907, fig. 20.

Inscriptions

Two marble inscriptions record a restoration of the mole that had collapsed due to the violence of the sea. The work was carried out by order of Antoninus Pius in 139 AD, but had already been promised by his father Hadrianus. The first inscription, now in the Archaeological Museum of Naples, was found in the sea near the mole in 1575, but fitted exactly in a cavity in one of the piers (width 2.48, height 1.43). The second one, which has disappeared, was still in the mole at the end of the 15th century. The inscriptions state that there were 20 piers and call the mole opus pilarum, "a work of pillars".

IMP(erator) CAESAR DIVI HADRIANI FIL(ius) DIVI TRAIANI PARTHICI NEPOS DIVI NERVAE PRONEPOS T(itus) AELIVS HADRIANVS ANTONINVS AVG(ustus) PIVS PONT(ifex) MAX(imus) TRIB(unicia) POT(estate) II CO(n)S(ul) II DESIG(natus) III P(ater) P(atriae) OPVS PILARVM VI MARIS CONLAPSVM A DIVO PATRE SVO PROMISSVM RESTITVIT	Top: EDR094073. 139 AD. Centre: EDR169092. 139 AD. Bottom: drawing of the second inscription in an old manuscript. Image: EDR.
[Imp(eratori) C]AESARI DIVI [Hadriani f(ilio) divi Traiani] [Part]HICI NEPOTI DIVI [Nervae pronep(oti) T(ito) Aelio Hadriano] [Ant]ONINO AVG(usto) PIO [pont(ifici) max(imo) trib(unicia) pot(estate) II co(n)s(uli) II p(atri) p(atriae)] [c]OLONIA FLAV[ia Augusta Puteoli] [quod s]VPER CETERA BEN[eficia a divo patre promis] [sum op]VS PILARVM VIGI[nti vi maris conlapsum splendore] [anti]QVO ET MVNITIO[ne adiecta restituit]