Khiva had existed as a fort and trading outpost on a branch of the Silk Road for several centuries before it rose to prominence in the sixteenth century as the capital of Khorezm Khanate. From this period it became important and notorious as a market for slaves captured from as far away as Russia. The Khivan khanate was subdued by imperial Russian armies in the late nineteenth century and was eventually absorbed into the Uzbek Soviet Socialist Republic in the 1920s. The small old city (Ichon-Qala) has intact mud walls dating from the 18th century (replacing earlier walls destroyed by Persian invaders) that are pierced by gates on four sides. Its historical sites, some of which are to be seen here, were extensively restored during the Soviet period. Khiva is now a UNESCO World Heritage Site.