the 6th century the province included 16 cities along the capital, Larissa: Demetrias, Phthiotic Thebes, Echinos, Lamia, Hypata, Metropolis, Trikke, Gomphoi, Caesarea, Diocletianopolis, Pharsalus, Saltos Bouramesios, Saltos Iovios, and the islands of Skiathos, Skopelos and Peparisthos. From the reign of Justin I () on, attacks on the imperial frontier on the Danube became more and more frequent, and the Balkan provinces were heavily raided, although Greece was less affected. In 539, however, a large Hunnic raid plundered Thessaly and, bypassing the fortified Thermopylae pass, devastated Central Greece. This led to a serious fortification effort under Justinian I (), and the establishment of a permanent garrison at Thermopylae. The area was once more invaded in 558 by the Kotrigurs, but they were stopped at the Thermopylae. Despite the devastation caused by these raids, in Thessaly, and southern Greece in general, the imperial administration seems to have continued to function, and traditional public life to have continued, for much of the century, possibly up to the end of the reign of Justin II (). Nevertheless, the barbarian raids, the two great earthquakes of 522 and 552, and the arrival of the Plague of Justinian in 541–544, led to a drop in population. Middle Ages Slavic invasions and restoration of Byzantine control The late antique order on Greece was irrevocably shattered with the Slavic incursions that began after 578. The first large-scale raid was in 581, and the Slavs appear to have remained in Greece until 584. Byzantium, confronted by long and bloody wars with Sassanid Persia in the east, and with the Avar Khaganate in the north, was largely unable to stop these raids. After the murder of Emperor Maurice in 602 and the outbreak of the great Byzantine–Sasanian War of 602–628, the Danube frontier, somewhat stabilized under Maurice, collapsed entirely, leaving the Balkans defenceless for the Slavs to raid and settle. The Slavic settlement that followed the raids in the late 6th and early 7th centuries affected the Peloponnese in the south and Macedonia in the north far more than Thessaly or Central Greece, with the fortified towns largely remaining in the hands of the native Greek population. Nevertheless, in the first decades of the 7th century the Slavs were free to raid Thessaly and further south relatively unhindered; according to the Miracles of Saint Demetrius, in the Slavic tribes even built monoxyla and raided the coasts of Thessaly and many