The actual military difficulties of the undertaking were not great, for though the Indians were brave and warlike, and though they had a well-populated land to draw from, they were not a national unity. As the Indian states were constantly at war with one another, there would be an opportunity of securing allies in the peninsula. There was no difficulty in securing recruits for the expedition, although it is true a large detachment of the army had well-understood motives for desiring to be left in Bactria; but some of the best Asiatic warriors from these regions were enrolled, 30,000 in number, and the levies with which Alexander now prepared to descend on India were certainly twice as great as those with which he had left Macedon seven years before. His army was now a great cosmopolitan community, an organism resembling the mercenary armies of the Middle Ages, in the times of the Condottieri. It was self-supporting and self-sufficient in more senses than one, for it included artisans, engineers, physicians, diviners, literary men, athletes, secretaries, clerks, musicians, as well as a host of women and slaves. Most of the states in northern India at this time were inhabited by what is often called an Aryan stock, the descendants of a succession of waves of emigration through the northwestern hills from central Asia. They had given up their nomadic life and reached the agricultural stage. The Brahman caste system, with its asceticism, and with its power of directive guidance in the state, according to the dictates of a religious sect, already dominated the life of India, and the country as a whole was made up of small principalities and village communities with no common bond of union. Alexander effected his entrance into this new world by marching from Nicæa (probably to be identified with Cabul) along the Cabul river and then proceeded through the now well-known Khyber Pass. For the purpose of securing his communications much time had to be spent in warfare with the brave inhabitants of the Himalaya Mountains. Many fortresses were taken, the most remarkable of these exploits being the capture of the rock of Aormas, which probably lies on the right bank of the Indus, some sixty miles above the junction of that river with the Cabul. The two tribes whose resistance gave the most trouble were the Aspasians and the Assacenes, dwelling in localities which can now be identified as being parts of Chitral in the Pangkan and Swat valleys.