Background: 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.
Question: The earliest mentions of Slavic raids are across what river?
Answer:<extra_id_0>.
<extra_id_0> River Danube<extra_id_1>