I want to know the answer to the following question:
What did the Byzantines help the Khazars with?
All the background I'm provided with is that "The Byzantines also helped the Khazars build a fortress at Sarkel on the Don river to protect their northwest frontier against incursions by the Turkic migrants and the Rus', and to control caravan trade routes and the portage between the Don and Volga rivers.". Is that enough to answer the question?