"The pressure of new circumstances led initially to large-scale slave-trading and the emergence of slave labour during the thirteenth and fourteenth centuries. The numbers of slaves in the Sultans' establishments were very high (50,000 under Alauddin Khilji, and 180,000 under Firuz Tughluq). Barani judges the level of prices by referring to slave prices, and the presence of slaves was almost all-pervasive."