In the eighteenth century Russia gained increasing control over the Kazakh Steppe. In 1839 they failed to conquer the Khanate of Khiva south of the Aral Sea. In 1847-53 they built a line of forts from the north side of the Aral Sea eastward up the Syr Darya river. In 1847-64 they crossed the eastern Kazakh steppe and built a line of forts along the northern border of Kyrgyzstan. 1864-68 they moved south from Kyrgyzstan, captured Tashkent and Samarkand and dominated the Khanates of Kokand and Bokhara. They now held a triangle whose southern point was south of Siberia and southeast of their supply bases on the Volga River. The next step was to turn this triangle into a rectangle by crossing the Caspian Sea. In 1873 they conquered Khiva. In 1881 they took western Turkmenistan. In 1884 the Merv oasis and eastern Turkmenistan were taken. In 1885 expansion south toward Afghanistan was blocked by the British. In 1893-95 they occupied the high Pamir Mountains in the southeast.