Background

News of Illyrian offensive preparations in 335 BC reached Alexander when he was probably in Agrianian territory. The Autariatae tribe under Pleurias planned to attack him from the north, Cleitus the Illyrian had risen in revolt and Glaucias had entered into an alliance and joined Cleitus' cause. Cleitus had occupied the city of Pelion, a fortified site in eastern Dassaretia, an Illyrian canton. Pelion lay on the Illyrian side of Wolf's Pass (Qafa e Ujkut). Since Philip's annexation of this part of Illyria, Little Lake Prespa lay on the Macedonian side. Pelion at the time was the strongest settlement in the region and it was favourably located for attacks into Macedonia.^[8]

Battle of Pelium

Alexander found that Cleitus had not only occupied Pelion but also the surrounding heights, which look down on the city and cover the approach to Wolf's Pass. It was evident that he was waiting for Glaucias to arrive. Alexander wanted to strike at Cleitus first. He therefore pitched and fortified a camp on the river Eordaicus in full sight of the Illyrians, and next morning he moved his army up to the wall of Pelion. This move brought the Illyrians down from the heights in order to attack the Macedonians in the flanks and the rear. Alexander promptly about-turned his army and routed the Illyrians.

Alexander decided next to build a wall around Pelion, so that he could blockade the city and his army could operate inside its own defences. Next day Glaucias, at the head of a large army, came from the plain of Koritsa through the Tsangon pass and joined forces with Cleitus. Alexander was heavily outnumbered and knew for the first and last time the bitter taste of failure. He acted at once, sending his baggage train of horse-drawn wagons with an escort of cavalry under Philotas to round up supplies in the plain of Koritsa. Glaucias having failed to guard the Tsangon pass with sufficient care, enabled the Macedonians to proceed about their foraging. Glaucias now rectified his mistake and occupied both sides of the pass in the hope of catching Philotas' foraging party on its return. Alexander divided his forces. Leaving sufficient troops with the Illyrian garrison penned up inside Pelion, he marched to the Tsangon pass with the Hypaspists, archers and Agrianians and two squadrons of cavalry, some 5,000 men in total, and cleared the pass. Glaucias' Taulantians did not even put up a fight, and the baggage train returned in safety.

The effect of this success could only be short lived in terms of supply. The troops of Glaucias and Cleitus seemed still to have caught Alexander in a difficult position for the Illyrians held the commanding heights with large numbers of cavalry, large numbers of javelin-men and slingers, and had heavy-armed infantry as well. The next morning Alexander's plan was not to retreat, but to advance through the middle of the Illyrian forces, thereby keeping them divided and his own men united. In order to do so, he had to deceive the Illyrians and then seize the narrow passage, namely the Wolf's pass, confined between the river on one side and high cliffs on the other side and admitting only four men abreast at its narrowest point.

Next morning the deception was achieved by a superb piece of drill. The Macedonians paraded on the flat plain, without its baggage train, but with its catapults, which led the Illyrians under Glaucias and Cleitus to expect an assault upon the walls of Pelion. The drill was executed by the phalanx in a solid block of men, 100 men wide and 120 men deep, and by a squadron of 200 cavalry on each flank. Glaucias had a grandstand view from the battlements of Pelion and the surrounding heights, was amazed by the precision of the drill and bewildered by the changing movements. Suddenly Alexander formed the left front of the phalanx into a wedge (embolon) and charged Cleitus' troops on the nearest slopes. The Illyrians fled at the mere onset on this attack. Next the Macedonians using warlike threats, forced Glaucias' army to withdraw towards Pelion.

Three days later Alexander mounted a night attack. The Illyrians had assumed that Alexander had fled for good, so had bivouacked their men over a wide area and had not built field defences or mount guards. Learning of their dispositions, the Macedonians came back at night, leading the Hypaspists, archers and Agrianians and two phalanx brigades (in all over 7,000 men). The Illyrians were devastated by the Macedonians who struck in a deep formation at the very end of the Illyrian line, killing many in their beds and started a panic which became a rout as the infantry line poured through the gap and rolled up the Illyrian line from east to west. Cleitus and that part of his army under his immediate command, escaped into Pelion, but the rest suffered the thoroughness of the cavalry pursuit which continued to the mountains of Glaucias' state, some 95 km away. Cleitus burnt Pelion in order to not let it fall into the hands of the Macedonians, and went to join Glaucias in the region of what is now Tirana.

Aftermath

The escape and victory of Alexander and his army brought home to the Illyrians how much had changed since they had brought Macedonia to its knees barely 50 years before under the command of Bardyllis. In 334 BC a number of Illyrian infantrymen served in Alexander's expeditionary force and many more Illyrian troops were later to serve Alexander in Asia. Glaucias though defeated by the Macedonians, survived as king for another 30 years.^[4]