Between the ninth and eleventh centuries a long-distance trade moved captives from the Slavic-speaking lands of central and eastern Europe into the Islamic Mediterranean, where they were known collectively as saqaliba. Captives taken in Ottonian and Frankish wars on the eastern frontier, and by Slavic rulers on each other, were bought by merchants and moved west and south through Prague and Verdun — the latter notorious in the Arabic and Latin sources as a place where boys were castrated for the eunuch market, an operation with very high mortality — and thence to al-Andalus, Ifriqiya and the eastern caliphate. In Umayyad Córdoba the saqaliba became a distinct military and administrative corps and, after 1009, a political force in the taifa period. The trade declined as the Slavic lands Christianised and their rulers stopped selling co-religionists. No quantities can be recovered; the evidence is Arabic geography, Latin toll records and the distribution of Islamic silver in northern hoards.
Frankish, Ottonian and Jewish long-distance merchants bought captives taken in wars on the Slavic frontier and sold them through Prague, Verdun and Mediterranean ports into al-Andalus, North Africa and the eastern Islamic world
The trade drew captives from shifting frontier zones between the Elbe and the middle Danube over roughly 300 years, and the evidence is toll records, coin hoards and Arabic geographers' descriptions rather than counts of either captives or source populations. Neither the number enslaved nor the population of the raided regions can be reconstructed with enough confidence to support a ratio.
No figures. Mortality from castration and from the long overland transit is described qualitatively in the Arabic sources as very high but was never counted.
Enslavement and transport of Slavic captives for military, domestic and sexual servitude is documented by Ibn Hawqal and other Arabic geographers and analysed in the Brill and IJMES scholarship cited.
Czechia, Poland, France, Spain