Accordingly the army of the emperor, instead of making an easy conquest of the Caucasus, was obliged to remain for the most part shut up in the chain of their miserable forts and kreposts. Here, when these fortified places were not boldly assaulted and carried by storm, as often happened, the troops fell a gradual prey to fevers and dysenteries, or to the want of those supplies which the peculation of the officers in charge of them continually either withheld or adulterated. The forts, situated on the coast of the Black Sea, could be relieved only during that half of the year which was suited for navigation; while those on the Kuban and the Terek were dependent on the precarious supplies conveyed overland at such times as the roads were passable. To keep up the spirits of the imprisoned garrisons the men were made to sing by word of command; and the dance was introduced as a military exercise. The Caucasus in fact became a southern Siberia, where the average life of the soldier was but three years. Taught at length by repeated and disastrous failures that this method of attacking the Circassians was a fatal error, the czar next adopted the plan of sending into the mountains heavy masses of infantry supported by powerful trains of field artillery. These with great labor penetrated a certain distance into the interior for the purpose of opening roads from one important fortress to another, and guarding them with chains of mud forts or kreposts. They made reconnoissances in various directions, succeeded in isolating and subduing some of the districts lying on the Kuban and Laba rivers, and completed the subjugation of the more open country of the Kabardan tribes, who were obliged to accept terms of neutrality.