"attired for the grand signior's seraglio"
The Seraglio
Public DomainThe Seraglio - Credit: John Frederick Lewis

A seraglio was the enclosed living quarters used by wives and concubines in an Ottoman household, the harem of a house or palace. 

"The Seraglio" may refer specifically to the Topkapi Palace, the residence of the former Ottoman Sultans in Istanbul.  Beautiful and intelligent slave girls were either captured in war (mainly Christian Europeans in the Balkans), recruited within the empire, or procured from neighbouring countries to become imperial concubines.