It was critical for Alexander to take this pass as it provided easy access to Illyria and Macedonia, which was urgently needed in order to quell the unrest in Greece at this time in Athens and Thebes.

Taking this pass allowed Alexander to march his army to southern Greece quickly, which would eventually result in the total destruction of Thebes.

News of the Illyrian revolt under the chieftain Cleitus and Glaukias of the Taulantii first reached the ears of Alexander while he was campaigning on the Danube against some of the northern tribes that his father, Philip II of Macedon had previously reduced to a satisfactory level of subjection, although not outright submission.

Alexander was immediately concerned about the news of this revolt, as the fortified settlement of Pelium itself occupied one of the most important passes between Illyria and Macedonia.

In addition to this, without access to this crucial pass, Alexander could be cut off from Greece, which had freshly revolted, and would eventually do so again, with aid of the Great King.

The loss of this pass, and the resultant long march would give the Greek city states to the south ample time to prepare for Alexander's arrival while he was reducing the Illyrians.

Langarus, of the Agrianians, made frequent incursions into the country of the Autariatae, and managed to put them on guard sufficiently to allow Alexander to march by in relative peace.

Seeking to seize his line of retreat before putting his shoulder to the siege, Alexander desired to attack the heights that commanded the defile through which he had come.

[5] He then drew up his phalanx, one hundred and twenty men deep,[5] with 200 cavalry on either flank, and arranged his soldiers to perform close-order drills down on the plain, in full view of the Illyrians, in complete silence.

As Peter Green describes: At given signals the great forest of sarissas would rise to the vertical 'salute' position, and then dip horizontally as for battle-order.

This sudden, shattering explosion of sound, especially after the dead stillness which had preceded it, completely unnerved Glaucias' tribesmen, who fled back in wild confusion from the foothills to the safety of their fortress.The Macedonian forces took the heights overlooking Pelium.

[7] After three days,[1] before reinforcements arrived, however, Macedonian scouts reported that they observed the Illyrians becoming careless in protecting the settlement, as they thought Alexander was in retreat.

[9]As a result of this siege, Alexander gained Pelium, and built a fresh outpost there, as the Illyrians had burnt the settlement that had previously been situated there.

Having completed his conquest, Alexander had established himself as a new monarch to be revered,[citation needed] and was now free to march south to Boeotia and deal with the threat from Thebes and Athens.