(...) Let us now move to one of the most mysterious and at the same time controversial issues concerning the geographical range of Slavic settlement in the Early Middle Ages. In publications describing Slavic homelands this issue - usually - has no answer to, or - at best - is briefly mentioned in passing. However, we really have numerous clues concerning this issue, which in our opinion cannot be ignored when discussing the history of Slavs in Eastern Europe. Let's thus take a look at surviving to our times testimonies suggesting the existence of Slavic settlement in the area of middle and lower Volga. Their authors were Muslims, who due to their trading and political areas of interest provided us as the only ones with accounts worthy of paying attention to. And so Ibn Hurdadbeh mentions: "... to Hamlih (Itil), which is located at the river flowing from the country of Slavs and draining into the Jurchen (Caspian) Sea...". Mentioned river is Volga. Under the name Nahr al Saqaliba (River of the Slavs), Volga is mentioned in the work of Ibn Hardadbeh several times. Apart from him also Ibn Atem-al-Kufi and Ibn Rusta - describing the Arab-Khazar conflict of the 730s - also call Volga like this. Moreover, Ibn Fadlan in his account from the diplomatic travel to Volga Bulgaria consistently (as many as 16 times! - which means that it could not be a technical or a factual mistake) calls the ruler of this realm Malik as-Saqaliba (King of the Slavs).
Equally mysterious news is provided by Al-Baladuri when he described rivalry between the Islamic world and the Khazars in the 8th century: "Marwan attacked the Slavs living in the land of the Khazars, and took into slavery 20,000 [Slavic] families". Another, often neglected by historians document allowing us to place the early homelands of the Volga Slavs is the letter of Khazar Kagan Joseph written to Spanish Jew Hasday ben Shaprut. In that letter we find an excerpt mentioning tribes living under the suzerainty of the Khazars: ".... Some of them live in open spaces, other in fortified strongholds. Here are their names: Bulgars, Savirians, Erzya, Cheremises, Vyatichi, Severians, [Volga] Slavs (!). All of them serve and pay them tribute."
(...)
... testimonies based on direct talks between Arab chroniclers and inhabitants of Kama Bulgaria: "Two Arab writers ad-Dimaski and Ibn al-Atir, basing on some older, unknown to us, source, quote a statement of a large group of Kama-Bulgarian Muslim pilgrims who traveled to Mecca in years 1041/1042. Asked by inhabitants of Baghdad, where they made a stop on their way to Mecca: who actually are the Kama Bulgars?, they answered, that this nation can trace their origins to Turks and Slavs."
(...)
"It is also worthy to quote information given by Yaqut in his Mu'gam al-buldan, where he wrote, that in Aleppo he met Muslim students, whose ancestors were from Kama Bulgaria, and they had fair skin and blonde hair."
(...)
Arab and Persian writers distinguished between Bulgar tribes from Eastern Europe and those from the Balkan Peninsula, calling the former al-Bulgar (Bolgar) and the latter Burdzan.
(...)
Neither Vyatichi, nor Krivichs, nor Ilmen Slavs were reaching the discussed region [Volga River] as early as the 8th century. Those areas were at that time inhabited by Meria, a tribe of Finnic origin and - which is less certain - remnants of Baltic population. (...) Therefore the suzerainty of Kama Bulgars over some groups of Slavic people did not refer to historical East Slavic tribes living far away to the west of them, [but to Slavs living at the Volga River].
(...)
Immediate western neighbours of Volga Bulgars were not Slavic, but Finnic: Mordvins, the Meshchera and Muromians.
(...)
In our opinion in the Early Medieval period in territories controlled by the Khazars or acknowledging their suzerainty lived two, or maybe even three, large groups of ethnic Slavic population. The first was located in the basin of Kama (and Vyatka) and was probably the remains from times when ancestors of Slavs had migrated from Asia to Europe*. An anonymous Arab source from late 9th/early 10th centuries contains, among many information about peoples of Eastern Europe, also this one: "between the land of the Pechenegs and that of Bulgar Slavs are the boundaries of the land of Magyars" - this excerpt describes situation in the late 8th century, time when Magyar homeland was still located in the vicinity of Southern Urals (at the Belaya River). It could mean that these Slavs should be identified with Slavs living at the Kama (middle Volga).
Lands located much more to the south, between the lower Don and the lower Volga, were also inhabited by Slavs (see: the account about Marwan's campaign against the Khazars). They settled in that region after the collapse of Great Bulgaria, perhaps under permission from rulers of Sarkel and Itil. They (or part of them) could also be invited or resettled there by some Turkic peoples, including the Khazars, who wanted to develop those sparsely populated and yet fertile lands by Slavs, as well as to protect those lands from dangerous Arab invasions. The collapse of mass Slavic settlement in that area took place most probably by the end of the 9th century, as the result the invasion by Pecheneg tribes, who - as far as we know - contrary to the Khazars or the Magyars, did not have great skills when it comes to cooperation with agricultural populations.
On the other hand in the middle Volga area ethnic Slavic element started to lose its distinctness, when Bulgars converted to Islam, abandoning their previous religious beliefs. The process of assimilation could last several hundred years, but by the time of the Mongol Invasion the last traces of Slavic ethnos were already rubbed away. (...)
It counts Volga Slavs as Slavs. 
