Siege of Pelium The Siege of Pelium was undertaken by Alexander the Great against the Illyrian tribes of what is modern day Albania . 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 . This was an important point of demarcation in Alexander ' s early reign , as it established him among the Danubian tribes to the north as a serious monarch to be reckoned with , just as he would later establish this precedent for the Greek city states under his hegemony . Taking this place allowed Alexander to march his army to southern Greece quickly , which would eventually result in the total destruction of Thebes . Background . News of the Illyrian revolt under Cleitus the Dardanian , and King Glaukias of the Taulanti 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 . As this area had been far from the Greek theatre of operations , Phillip had been satisfied with the level of subjection he had reduced them to . Alexander was immediately concerned about the news of this revolt , as the settlement of Pelium itself occupied one of the most important passes between Illyria and Macedonia . As a result of this , Alexander would have to make a long march around a mountain range to the south , and then into Illyria . 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 . An ally of Alexander offered aid to him by protecting his flank from barbarian tribes while he marched towards Pelium . Langarus , of the Agrianians , made frequent incursions into the country of the Autariatians , and managed to put them on guard sufficiently to allow Alexander to march by in relative peace . Having successfully made this march , Alexander arrived to find Cleitus the Dardanian in control of Pelium and awaiting the arrival of King Glaukias with reinforcements . When Alexander arrived , Cleitus reportedly sacrificed three boys , three girls , and three black rams before meeting the Macedonians . Opening . Alexander arrived with 15 , 000 soldiers and determined to attack Pelium at once , as he hoped to take the place out of hand before King Glaukias could arrive and reinforce Cleitus . The first thing Alexander did upon arriving was set up the Macedonian camp . The Macedonians found that not only was Pelium itself held , which commanded the plateau , but the heights surrounding the Plain of Pelium was held in force . Upon completing the camp , Alexander resolved to attack the troops of Cleitus that were surrounding the heights . This he did with some effect , and as a result of this assault the barbarians retreated within the walls of Pelium . Alexander then attempted to take the town by assault , but failing in this , he started to erect circumvallation and contravallation around Pelium . This however , was interrupted by the arrival of Glaukias and his reinforcements the next day , which compelled Alexander to retreat from the heights that Alexander had captured the day before . Battle and Siege . Having been forced back into the plain itself by King Glaukias , Alexander was in now a perilous situation . He was outnumbered by the barbarians , who were free to gather supplies . Not only that , but Alexander was anxious to taking Pelium quickly before Thebes and Athens could seriously consider throwing off Macedonian hegemony . Therefore , not only did Alexander have pressing issues elsewhere , but the barbarian forces were bent on the annihilation of Alexander ' s forces , and could afford to wait . Being short of supplies , Alexander sent Philotas , one of his lieutenants , out to forage for supplies . Glaukias witnessed this force leaving , and pursued and attacked the foragers . However , Alexander was with some difficulty able to fend off the attackers and extricate his hypaspists , Agrianians and bowmen . 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 . This defile was small , and only four men could march through it abreast . He therefore decided upon a singular method of attack . He drew up some of his infantry and cavalry in front of the settlement of Pelium itself to defend this maneuver from being attacked by a sortie from Cleitus . He then drew up his phalanx , one hundred and twenty men deep and started to drill his soldiers in the plain below the heights . Alexander marched them towards the heights where King Glaikus troops were stationed , who were watching his troops drill below them with surprise . Suddenly , Alexander drilled his phalanx into a wedge and charged them up the heights , forcing the shocked barbarian troops to retreat . During this engagement , not a single Macedonian armored soldier was killed . However , deaths among light troops were usually not reported , and it is unknown whether any were killed in this instance . However , there were still some barbarians on the heights that commanded the ford , and it was critical for Alexander to seize these heights in order to control of the entire plain . Before engaging in battle , Alexander decided to re - establish his camp on the far side of the river near the ford , in order to ensure the security of both his operations and his camp . However , in the process of doing so he ran the danger of being taken in the rear while his troops were crossing the river , and the barbarians attacked him , perceiving his army to be retreating . So he ordered his troops to turn around to simulate an advance , while initiating a charge with his companion cavalry . Meanwhile , he also ordered his archers to turn around and fire their arrows at the barbarians from mid stream . Having gained a place of safety on the far side of the river , Alexander was able to freely supply his army and await reinforcements . Before reinforcements arrived , however , Alexander ' s scouts reported that they observed that the barbarians were becoming careless about protecting the settlement , as they perceived that Alexander was in retreat . Acting on this intelligence , Alexander awaited the arrival of night , and then rushed ahead without awaiting the crossing of his complete force , leading his shield - bearing guards , the Agrianians , archers and the brigade of Coenus as the leading unit . He then rushed down upon the defenders with his Agrianians and archers , who were formed in phalanx formation . Many of the barbarians were still asleep , and were taken completely by surprise . A slaughter followed , many of the barbarians were captured . Result . As a result of this siege , Alexander gained Pelium , and built a fresh outpost there , as the barbarians had burnt the settlement that had previously been situated there . The barbarians begged for terms , and Alexander was happy to accept their submission and allow them to swear fealty to him anew . Having completed his conquest of these particular tribe of barbarians , Alexander had established himself as a new monarch to be reckoned with , and was now free to march south to Boeotia and deal with the threat from Thebes and Athens .