Unable any longer to cope with his adversaries in the open field, Ibn-Abu adopted the more effective policy of guerilla warfare. His army, divided into strong detachments, was posted at advantageous points whence the operations of the enemy could be observed and communication easily maintained. In this way the invaders were placed at a great disadvantage. The Moors retired before their advance; the towns were evacuated; all property was removed or concealed; convoys were cut off; and the army of the Duke of Sesa, who commanded the Christians, was almost reduced to extremity by famine. It became absolutely necessary to establish a base of supplies, and the Marquis of Favara was despatched with a considerable force to Calahorra. The Spaniards reached their destination in safety; but their movements had not escaped the vigilance of the mountaineers; and their return march, conducted without the precautions adopted by every wise commander, encountered an ambuscade in the valley of Ravaha. Here the road, so constructed that four men could with difficulty move abreast, was blocked by loaded beasts of burden, purposely left there by the Moors; and the soldiers, tempted by the hope of plunder, broke into disorder to seize them. The measures of Ibn-Abu had been taken with consummate skill. The Spaniards, hopelessly entangled in the narrow defile and completely surrounded, were ruthlessly slaughtered. In former attacks the mountains had always resounded with the piercing war-cries of the assailants, but now not a sound, save the scattering reports of arquebuses and the whistling of arrows, broke the ominous stillness of the scene. The advance guard and the centre had been destroyed before the Marquis was even apprized of the presence of an enemy. He effected his escape only by superhuman exertion, and of the sixteen hundred soldiers who composed his command fourteen hundred atoned for the military crimes of official negligence and disregard of discipline. On the Moorish side not a man was killed, and less than twenty were wounded. History affords but few parallels to the battle of Ravaha when both the numbers engaged and the immunity of the victors are considered.