Sarkel (or Sharkil, literally white house in Khazar language) was a large limestone-and-brick fortress built by the Khazars with Byzantine assistance in the 830s. Sarkel was located on the left bank of the lower Don River, in present-day Rostov Oblast of Russia.
Sarkel was built to protect the north-western border of the Khazar state in 833. The Khazars asked their ally, Byzantine emperor Theophilus, for engineers to build a fortified capital, and Theophilus sent his chief engineer Petronas. In recompense for these services, the Khazar khagan ceded Chersonesos and some other Crimean dependencies to Byzantium. Historians have been unable to determine why such a strong fortress was built on the Don. 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. Other historians believe this polity was situated many hundred miles to the north. Another nascent power, the Magyars, was not particularly threatening to the Khazars as long as they paid tribute to the khagan.
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; the route was known as the " Khazarian Way". A garrison fortified at Sarkel included Oghuz and Pecheneg mercenaries. Sarkel's fortress and city were captured by Kievan Rus' under prince Sviatoslav I in 965. The city was renamed Belaya Vezha (Slavic for White Tower or White Fortress) and settled by Slavs. It remained Slavic until the 12th century, when the district was taken over by the Kipchaks. Mikhail Artamonov excavated the site in the 1930s. It was the most ambitious excavation of a Khazar site ever undertaken. Among many Khazar and Rus items, Artamonov discovered Byzantine columns used in the construction of Sarkel. The site is now submerged by the Tsimlyansk Reservoir, so no further excavations may be conducted.