Portus Cosanus	February 19, 2003
by Mark Rose

Exploring a Roman port and fishery

Artist's reconstruction shows how the Port of Cosa might have appeared during its heyday, the late second and first centuries B.C. (Drawing by Kathleen K. Borowick, courtesy A.M. McCann) [LARGER IMAGE]

In the first half of the third century B.C., the Roman Republic was expanding. The conquest of the Etruscans, to the north, and of the Greeks, to the south, would give them control of the entire Italian peninsula. To solidify their control, the Romans established colonies along the Tyrrhenian coast of their new territories. The port of Cosa, the earliest Roman port thus far known, was founded in 273 B.C. and was the reason for the establishment of the colony about 140 km north of Rome. The port, below the fortified hill town, enjoyed the protection of one of the few promontories along this predominantly sandy coastline and was the area's only source of freshwater. Behind the harbor was a rich lagoon where excavations have revealed evidence of a large commercial fish farm.

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The colony was founded to take advantage of a natural harbor below a promontory (viewed from west, left). Behind the harbor was a lagoon, now mostly filled in (viewed from east, right), which was the site of an extensive fishery in antiquity that has been revived today. Note modern fish ponds in the foreground. (Courtesy A.M. McCann)

Excavation of the town, beginning in the late 1940s by the American Academy in Rome, and of the harbor, in the 1960s and 1970s by Anna Marguerite McCann, revealed Cosa's changing role over the centuries: from a colony, to a bustling marine export center for wine and fish products, to an import center for luxury goods required by the surrounding Imperial villas. The history of Cosa, as revealed by archaeology, reflects Rome's conversion from an agricultural based Republic to a maritime commercial superpower.

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Aerial view shows Roman breakwater extending from promontory with concrete pier for base of lighthouse seen underwater at the end (left). Excavation revealed Roman pottery beneath boulders of breakwater extension E (right). (Courtesy A.M. McCann)

Soon after the colony was founded, the large breakwater of the harbor was constructed from limestone blocks extending about 110 m out from the cliffs. As early as the late third century B.C., amphoras--the terra-cotta shipping containers of antiquity--were being produced at Cosa. Many of these are stamped with the symbols of the Sestii, a powerful Roman family that Cicero writes had a villa at Cosa. This long-lived family came to dominate trade in the western Mediterranean from the early second through the first centuries B.C. The Sestii probably also financed the port and fishery, running the wineries and producing the amphoras in which the vintages were shipped. They likely also controlled the fishery and saltery where the famous fish sauce of the Romans known as garum was made from the guts of fish left to ferment in the hot Mediterranean sun. Cosa gives us the first evidence for the export by the Romans of this salty condiment that was on every Roman table.

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Taking advantage of a natural fracture in the bedrock, the Cosans cut this channel, known as the Tagliata, to control the flow of water into and out of the lagoon and to harvest fish (left). A concrete holding tank and cane enclosure in a modern lagoon fishery at Lago di Burano are likely similar to ancient fishery facilities at Cosa (right). (Courtesy A.M. McCann)

Now mostly silted over, the ancient lagoon at Cosa originally stretched for 20 km, was up to 800 m wide, and 5 m deep. Such coastal barrier lagoons are found elsewhere in Italy only near Venice and today are still one of Italy's richest natural resources yielding eel, gray mullet, sea bass, and sole. The fisheries at nearby Orbetello and the modern fishery in the western end of the Cosa lagoon area continue this ancient tradition today.

Cosa reached its height in the later second and early first centuries B.C. It is during this time that the massive concrete piers of the harbor still visible today were built as well as the concrete remains in the lagoon. These included a spring house that supplied fresh water for the fish farm, and the port with its amphora factory and saltery. The Romans learned that when pozzolana, a powdery volcanic ash imported from Pozzuoli, ancient Puteoli, was mixed with lime and water it makes a tenacious binding material that sets and endures in salt or fresh water. The pozzolana concrete structures at Cosa are our earliest examples of this revolutionary building material invented by the Romans and used until the invention of Portland cement in modern times.

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Remains of an elaborate spring house were excavated at the west end of the lagoon (piers of aqueduct, spring house in center, cistern at back). Water was lifted from the spring house to the cistern using a bucket-chain wheel, probably powered by slaves. (Courtesy A.M. McCann)

The most important single find from the Portus Cosanus was the unique wooden water-lifting mechanism that lifted water from the spring house to an aqueduct that served the port in its prime during the second and first centuries B.C. In early Imperial times the spring house was refurbished and a new water wheel lifted water to a cistern serving a bath and the maritime villa that now occupied Cosa's shore. The Cosa bucket chain is the earliest archaeological evidence we have for this sophisticated water-lifting technology, which was probably developed in Alexandria in the third century B.C. and imported by the Romans. It is still used in parts of the Near East today known by its Arabic name, saqiya.

Cosa's heyday was not to last. The fortified hill town was destroyed, perhaps by Cilician pirates, around 70-60 B.C., though the port continued to prosper. But the spring house was abandoned in the late first century B.C., perhaps after a great storm or tidal wave blanketed the harbor and fishery with and heavy layer of sand. Reprisals against Lucius Sestius, who supported Brutus in 42 B.C. during the civil war after Caesar's assassination, may have disrupted the port's economic life. In a larger sense, however, Rome's needs had changed. It was now an importer of goods coming from the south which flowed into Ostia: grain for its growing population and luxuries demanded by the Imperial court and aristocracy. By the start of the Imperial period in 27 B.C., the need for Cosa as an export hub to the north had passed. The second half of first century A.D. saw the harbor no longer a great export center for wine and garum, but rather a local harbor used for the import of goods by the elaborate maritime villa that now overlooked the sea on which the Sestii had earlier made their fortunes.

For more on Cosa, see A.M. McCann's, The Roman Port and Fishery of Cosa: A Short Guide (Rome: American Academy in Rome, 2002). McCann has brought the research on this major archaeological site she previously published with her colleagues (The Roman Port and Fishery of Cosa: A Center of Ancient Trade, Princeton University Press, 1987) up-to-date in a beautifully illustrated book useful to both laymen and scholars. The book includes an Italian translation and all profits are being donated to the Archaeological Institute of America. Available from David Brown Book Company.

Mark Rose is executive and online editor of ARCHAEOLOGY.

© 2003 by the Archaeological Institute of America archive.archaeology.org/online/features/cosa/