At www.q-mag.org/a-germanic-harbor-town-found-at-the-mouth-of-the-elbe-rive… … apparently, mainstream hasn't been looking or thinking of Romans ensconced in the wetlands around the mouth of the Elbe River so it has been somewhat of a surprise to find a settlement there, from the Roman period right up to around 1000AD. At the latter date the site was abandoned – did it have anything to do with the tsunami wave that ran up the English Channel in 1014AD? It had managed to survive the rising sea levels of the Late Roman/early Saxon era (known as the Dunkirk Transgression event in the Netherlands) but was overwhelmed just as the Medieval Warm Period had kicked in (when the climate was drier). It could of course have been sacked by the Vikings – but no mention of this appears in the article. The abandonment is left as a mystery – with people moving upstream to towns such as Hamburg.
According to Pliny the area around the Elbe estuary was too wet – and no doubt got even wetter in the Late Roman period. He said the Chauci tribes erected earthen banks and dykes (much like the Dutch more recently). Fish, stranded in pools behind the dykes after the tides went out were a staple food item of the locals. Archaeologists, until now, did not bother much in looking at the wetlands, taking what Pliny said to heart. Aerial photography was the first clue that a large settlement existed there, subsequently confirmed by excavations. A large town with a harbour has been unearthed. Coins, beads, pottery sherds, and even a chunk off a bronze statue has been unearthed, many of them dated to the Roman era. It seems the locals were cultivated by the Romans. The idea was to prize the elite with luxury items in order to get their co-operation and support – much as they did elsewhere on the borders of their empire, including Britain (before it was conquered). The harbour remained in use right up to the 11th century.
At https://phys.org/print426753611.html … we have news of another ancient site – this time off the coast of Cyprus. It too was swamped by water – and lies submerged. Again, the Roman empire period is featured, and the whole period between the end of the Bronze Age until the end of the Roman empire.