On the Antiquities of Prussia

...nor iron; if they ever joined battle among themselves, they used sharpened stakes and poles. But not many years had passed while the Germans inhabiting Hulmigeria, having regained their strength—for they had been greatly worn down by the Goths—and having summoned allies from across the Vistula, who crossed the river in boats and settled among them, prepared wars against the Borussii with joined forces. Entering the harsher parts of the region, they either took into servitude or forced to retreat as many of the Borussii as they encountered, and in a short time they secured themselves and their own from the fear of the barbarians. But the Borussii, so that they might be safer from the bordering Germans, entered into an alliance with the Sudini, who have settlements beyond the currents of the Chronus and are believed to be the aborigines of that region; they were then very powerful in virtue and strength. The Chronus is a river which today is called the Pergulus, which originates in the borders of Borussia toward the winter solstice, formed by many lakes flowing into one another in almost the same place. It separates the Borussii, first from the Samii (to use Strabo’s name), and then from the Sudini—peoples who were also tested more than conquered by Roman arms. For they were attacked by fleets under Drusus Germanicus, as Pliny testifies. He was the first of the Roman leaders to enter the northern ocean, and after him, Domitian Caesar, during the expedition he undertook against the Sarmatians because they had killed a legion along with its legate, [did so] on account of amber, which the barbarians there, among all peoples, were the only ones to gather from the things cast up by the sea, and in greater abundance.