The city fell an easy prey, and they bent their steps homewards, dragging with them a vast amount of booty, and a thousand of the most beautiful inmates of Khivan harems. Their cupidity was their ruin, for they were overtaken by the incensed husbands, and cut to pieces. A still worse fate was encountered during a later raid; for the Cossacks who undertook it lost their way, and were overtaken by winter on the wind-swept shores of the Aral. To such straits were they reduced that they had recourse to cannibalism.[533] But the stream of Russian immigration continued steadily eastwards. Irkutsk was founded in 1661, and before the end of the century the northern limits were pushed forward to the polar ice. The southern boundary, however, was conterminous with steppes occupied with Mongolian nomads, and was open to their incursions. No part of his immense empire escaped the notice of Peter the Great. In the brief leisure left him by his self-imposed task of reform he did not neglect his Siberian possessions.[534] He perceived the necessity of giving them a defensible frontier, and of securing commercial relations with the Khānates of Khiva and Bokhārā, in order to pave the way for an intercourse with China and the Indies. With this aim in view he took counsel of an adventurer named Khwāja Nefes, who had studied in Samarkand and Bokhāran colleges, and was well acquainted with the politics of the Khānates. Under his promptings, Peter sent congratulations to the Khān of Khiva on his accession. His overtures were welcomed by that sovereign, who was hard pressed by the legions of Bokhārā. He sent an embassy to Peter,[535] offering to accept his suzerainty in return for protection against his powerful neighbours. The great reformer had too many cares nearer home to permit of his taking immediate action on this tempting offer, and it was not till 1714 that he was reminded of his distant vassal’s existence by another embassy, the object of which was to induce the Tsar to build a chain of forts on the east of the Caspian as a protection against Turkoman raids. Peter was now convinced that the time had come for effective interference in Central Asian affairs. He cast about him for an instrument, and found one in a young Circassian chieftain who had changed his name from Dawlat Girāy to Bekovitch Cherkaski on his conversion and baptism, and had been given a commission in the famous Preobajinski regiment, with the title of prince. The Tsar appointed him to the command of an exploring expedition, the objects of which were enumerated in a decree of the 29th May 1714. Bekovitch was enjoined to congratulate the Khān of Khiva on his accession, and to confirm him in his acknowledgment of Russian suzerainty. He was to explore the lower reaches of the Sir Daryā for gold, and ascertain whether it was practicable to reopen the old course of that river into the Caspian on the south of the Balkan range. Bekovitch’s voyage of discovery began in 1715.