Read this: 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.

No archaeological evidence of a Slavic settlement in the Balkans could be securely dated before when?
What is the answer? (If it cannot be answered, return "unanswerable")
c. 600 AD