Sarkel (or Šarkel, literally "white house" in the Khazar language[1][2]) was a large limestone-and-brick fortress in what is now Rostov Oblast of Russia, on the left bank of the lower Don River.

They generally assert that the costly construction must have been due to the rise of a strong regional power that posed a threat to the Khazars.

Alexander Vasiliev and George Vernadsky, among others, argue that Sarkel was built to defend a vital portage between the Don and the Volga from the Rus' Khaganate.

Constantine Porphyrogenitus records in his work De Administrando Imperio that the Khazars asked the Emperor Theophilos to have the fortress of Sarkel built for them.

In the 10th century, a Persian explorer and geographer Ahmad ibn Rustah mentioned that the Khazars entrenched themselves against the attacks of the Hungarians.

The city served as a bustling commercial center, as it controlled the Volga-Don portage, which was used by the Rus to cross from the Black Sea to the Volga and thence to the Caspian and Baltic.