In addition, remains of fish tanks have been found which suggest the importance of aquiculture and the production of garum. The port's main period of prosperity occurred from the late 2nd century BC through the later 1st century BC, and there was a revival by the 2nd and 3rd centuries AD due to the growth of the villa economy in the countryside of Cosa. Although the city of Cosa and the port must have interacted in important ways, material evidence indicates that they do not follow a parallel development. Archaeological methods and evidence The port at Cosa was first surveyed by Professor Frank E. Brown of the American Academy in Rome in 1951. According to Anna Marguerite McCann, one of the later excavators, "in antiquity Cosa was a landlocked port, communicating with the sea by means of an artificial ship-channel, protected at the seaward end by a massive breakwater and provided with a set of elaborate channels cut into the limestone cliff, designed to keep the mouth free of sand." Another lead excavator, Colonel John D. Lewis, invented two new technical devices: a water jet prober to help identify structures buried in the sand, and a construction of sheet steel formed by joining cylinders which could be used to obtain harbor stratification. This allowed finds to be recovered in a stratified context for the first time in underwater archaeology, and established ancient harbor levels for Cosa between one meter and one meter eighty below the current sea floor. Many fragments of transport amphorae have been found on the beach and offshore areas of the harbor, the earliest of which date to the late 3rd century. This provides support for the belief that there was a lucrative wine trade based in the Cosa area, especially because many of the amphorae were stamped with the sign of the Sestius family, major exporters of wine whose trade network extended into Gaul. The earliest Sestius amphorae found at Cosa date to 175-150 and continue into the 1st century. The abundance of Sestius amphorae fragments suggest that the port of Cosa was likely the center of manufacturing and distribution of these famous jars, which firmly places Cosa as a key trading center during the late Republic. Outer harbor There are visible remains of five large masonry piers in the outer harbor, which are built from mortared rubblework of tufa and sherds. The sherds are mostly