Greek harbour works were largely adaptations of natural anchorages: moles, quays and ship sheds. The ship sheds at Zea in the Piraeus are the most informative survival, because their dimensions constrain what a trireme can have been.
Roman practice was different in kind, because Roman concrete sets underwater. Volcanic ash from the Bay of Naples, mixed with lime and seawater, produces a hydraulic mortar that cures without air — which allows a mole to be built out into open water rather than assembled from dumped rubble.
The largest applications are Portus, the artificial harbour complex built for Rome by Claudius and Trajan when Ostia could no longer handle the traffic, and Caesarea Maritima in Judaea, where Herod built a major port on a coast with no natural shelter at all.
What the evidence supports
Harbour capacity and traffic volumes are not recoverable.
Basin areas can be measured, but how many ships used a port, how long they stayed and what they carried is estimated from amphora finds and from a handful of texts. Figures quoted for ancient port throughput are reconstructions.
Roman marine concrete cures underwater.
The pozzolana reaction is described by Vitruvius and Pliny and has been confirmed by analysis of cores drilled from surviving Roman harbour structures.
Ship shed dimensions constrain reconstructions of the trireme.
The sheds at Zea set an upper bound on hull length and beam, which is why they matter to a debate about a ship type of which no hull survives.
Caesarea was built where no natural harbour existed.
Attested by Josephus and confirmed by underwater survey of the submerged moles.
Examples
The evidence level on each answers how we know what the building looked like, not whether it existed.
- Evidence level: Documented
Near Ostia · Claudian, extended under Trajan
Portus
Trajan's hexagonal basin is still visible from the air. Built because the Tiber mouth could not handle Rome's grain supply. The hexagonal basin survives as a landscape feature and has been surveyed and excavated.
- Evidence level: Documented
Piraeus, Athens · 5th–4th century BCE
The ship sheds at Zea
Slipways for the trireme fleet, partly submerged. Their dimensions are direct evidence for the ships they held. Excavated, partly submerged, with the slipway cuttings measurable.
- Evidence level: Documented
Judaea · 22–10 BCE
Caesarea Maritima
Herod's artificial harbour, built with hydraulic concrete on an open coast. The moles have subsided and been excavated underwater, and concrete cores drilled from them preserve the original mortar.
Primary sources
Vitruvius, On Architecture 2.6, 5.12
Pozzolana and its behaviour, and construction in water.
Josephus, Jewish Antiquities 15.331-341
The construction of the harbour at Caesarea.
How to read the evidence labels
- Evidence level: Documented
- Supported by a named primary text or by excavated material evidence.
- Evidence level: Probable
- Supported by strong inference that most specialists accept.
- Evidence level: Disputed
- Substantial specialist disagreement exists; competing readings are stated.
- Evidence level: Literary
- Belongs to poetic or mythological construction rather than to history.
- Evidence level: Mythological
- Belongs to shared religious or mythic tradition rather than to any single text.
- Evidence level: Unknown
- The available evidence is insufficient to decide.
These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.