The earliest mentions of Slavic raids across the lower River Danube may be dated to the first half of the 6th century, yet no archaeological evidence of a Slavic settlement in the Balkans could be securely dated before c. 600 AD.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): The earliest mentions of Slavic raids are across what river?
River Danube