Located on the Silk Road, Bukhara has for three millennia been a center of trade, scholarship, culture and religion. During the golden age of the Samanids, Bukhara became the intellectual center of the Islamic world. Part of the Persian Empire for several centuries, it is today mostly populated by Tajik-speakers. The historic center of Bukhara, which contains numerous mosques and madrassas, has been listed by UNESCO as a World Heritage Site.