Great Gothic Seaborne Raids

The Great Gothic Seaborne Raids (267-269 CE) were a sequence of attacks on the Eastern Roman Empire by large Gothic Fleets. They were finally defeated by Claudius II Gothicus at the Battle of Naissus (268-9 CE)

In 267 CE, with a Fleet of 500 Ships, the Heruli attacked the cities of Byzantium and Cyzicus on the Black Sea Coast.
Despite being defeated by the Roman Navy they escaped into the Aegean and devastated Achaea.
They sacked the islands of Lemnos and Scyros and the cities of Athens, Corinth, Argos and Sparta.

This time a great alliance of Goths and Scythians under the Heruli with 2,000-6,000 ships and 325,000 men according to Zosimus.
They attacked the cities of Byzantium and Chrysopolis which were sacked, although they lost a large part of their fleet, they then passed into the Aegean and laid waste to Crete and Rhodes.
Their army besieged Thessalonica and Cassandreia. As the Emperor Aurelian approached, they retreated through Macedonia, plundering as they went.

In either 268 or 269 CE, at the Battle of Naissus, a Roman Army under the Emperor Claudius II Gothicus arrived from the north.
The Goths were decisively crushed and lost 30-50,000 soldiers.
After this, the Balkans and the Danube were quiet for several decades.