I want to know the answer to the following question:
Near what river were the Avars originally based?
All the background I'm provided with is that "In the 560s the Avars began to expand from their base on the north bank of the Danube; by the end of the 6th century they were the dominant power in Central Europe and routinely able to force the eastern emperors to pay tribute.". Is that enough to answer the question?