Slavery was a legal and important part of the economy of the Ottoman Empire and Ottoman society until the slavery of Caucasians was banned in the early 19th century, although slaves from other groups were allowed. In Constantinople (present-day Istanbul), the administrative and political center of the Empire, about a fifth of the population consisted of slaves in 1609. Even after several measures to ban slavery in the late 19th century, the practice continued largely unfazed into the early 20th century. As late as 1908, female slaves were still sold in the Ottoman Empire. Sexual slavery was a central part of the Ottoman slave system throughout the history of the institution.