While such were the aggressions of Macedonian officers in the exercise of their new imperial authority, throughout Greece and the islands—and such the growing manifestations of repugnance to it at Athens—Alexander had returned home to push the preparations for his Persian campaign. He did not however think it prudent to transport his main force into Asia, until he had made his power and personal ascendency felt by the Macedonian dependencies, westward, northward, and north-eastward of Pella—Illyrians, Pæonians, and Thracians. Under these general names were comprised a number[55] of distinct tribes, or nations, warlike and for the most part predatory. Having remained unconquered until the victories of Philip, they were not kept in subjection even by him without difficulty: nor were they at all likely to obey his youthful successor, until they had seen some sensible evidence of his personal energy. [55] Strabo speaks of the Thracian ἔθνη as twenty-two in number, capable of sending out 200,000 foot, and 15,000 horses (Strabo, vii. Fragm. Vatic. 48). Accordingly, in the spring, Alexander put himself at the head of a large force, and marched in an easterly direction from Amphipolis, through the narrow Sapæan pass between Philippi and the sea.[56] In ten days’ march he reached the difficult mountain path over which alone he could cross Mount Hæmus (Balkan.) Here he found a body of the free Thracians and of armed merchants of the country, assembled to oppose his progress; posted on the high ground with waggons in their front, which it was their purpose to roll down the steep declivity against the advancing ranks of the Macedonians. Alexander eluded this danger by ordering his soldiers either to open their ranks, so as to let the waggons go through freely—or where there was no room for such loose array, to throw themselves on the ground with their shields closely packed together and slanting over their bodies; so that the waggons, dashing down the steep and coming against the shields, were carried off the ground, and made to bound over the bodies of the men to the space below. All the waggons rolled down without killing a single man. The Thracians, badly armed, were then easily dispersed by the Macedonian attack, with the loss of 1500 men killed, and all their women and children made prisoners.[57] The captives and plunder were sent back under an escort to be sold at the seaports. [56] Strabo, vii. p. 331 (Fragm.); Arrian, i. 1, 6; Appian, Bell. Civil. iv. 87, 105, 106. Appian gives (iv. 103) a good general description of the almost impassable and trackless country to the north and north-east of Philippi.