After a quick campaign to secure his throne in Thessaly, most scholars agree that it was sometime in spring, 335, that Alexander was able to move north against tribes that had been in rebellion since they heard of Philip's death months before.

As soon as possible in the new campaigning season, Alexander took his army into Thrace, on the eastern border of Macedonia. The Thracian Triballi tribe, as well as the Illyrians to the west, were testing the strength of the new regime. As their lands lay north of his supply routes for the proposed Persian invasion, as well as the threats they represented for the very survival of Macedon, prompt action was critically necessary.

As usual, when Alexander commanded an army, it moved with remarkable swiftness. The Triballians lived south of the Danube river in the modern province of Pleven, in mountainous terrain. One of the first encounters could have been decisive: as Alexander's men marched through a defile at the foot of the mountains, they realized that the Treballi had seized the high ground and had manouvered heavy carts onto the heights, which could be used as weapons against the Macedonians and Greeks far below. Throwing the heavy carts down the mountain side, they became effectve missiles. Alexander thought quickly: "His orders were that those sections of the heavy infantry which had room enough were to break formation when the carts came tearing down the slope, and so let them through." Heavy-packed infantry were to lie flat on the ground with their heavy shields locked above their heads, so the carts would strike the metal wall and bounce off. Both tactics worked; the Macedonians didn't lose a man. Alexander then managed a neat counter-attack, using his infantry, his archers, and his Guards - the enemy fled and over a thousand died.

Crossing the ridge, Alexander then proceed across the Haemus mountains towards the Danube river, where he found that Syrmus, King of the Triballians, had sheltered his stores and noncombatants (and later, himself) on an island in the middle of the river. The Triballian rear-guard were again defeated as they skirmished at the approaches to the river. There was no opposition as Alexander reached the Danube. He had arranged for his navy to send ships to help in the attack on "Pine Island", but found that the steep sides of the island made it impossible to coordinate an effective attack. He promptly changed his plan to take the action to the tribes on the opposite side of the Danube, the Getae.

Here, in May, 335 BC, is the first use in Arrian of the magic Greek word, pothos regarding Alexander's actions - he describes Alexander's passionate 'yearning' to cross to the other side of the river, not only to attack, but just to discover what was there. Across the Danube was a large force of foot and cavalry - perhaps 14,000 men - to dispute the crossing. With cunning, Alexander chose to cross his army at night; as there were insufficient boats, he had his men fill their leather tents with plumped hay, using them as flotation devices to swim the river (few, if any, of the Macedonians could swim). At dawn, the Macedonian cavalry charge broke the warriors of the Getae, who fled from the nearby town with their women and children. After his successful coup, Alexander plundered the town and razed it to the ground so it could not be a magnet for further revolt.

Then, "...Alexander offered sacrifice on the banks of the Danube to Zeus the Saviour and Heracles, not omitting the River himself for allowing the passage." (Arrian, The Campaigns of Alexander, 4).

Here, as throughout all of his campaigns, Alexander was meticulous in following (and often, preceding) a military clash with priestly sacrifices to those gods whom he felt were particularly to be honored. Zeus and Heracles were among the best-loved of his personal pantheon, but he often sacrificed - as here, to the river - to local deities that also deserved honor. As both king and priest for his army, Alexander performed daily oblations to the gods, even when he had to be carried to do so, due to wounds or illness. His actions on the Danube prefigured a life-long humility before the gods in war.

Alexander now made for Pelium on the river Erigon in Illyria, a town occupied by the rebel leader, Cleitus. Before the battle, Alexander drew up his entire army, "...in mass formation 120 deep, posting on either wing 200 cavalrymen, with instructions to make no noise and to obey orders smartly." (Arrian, 6) Shouting to the infantry to raise their spears, Alexander then put his army through infantry manouvers and intricate drill which deeply intimidated the watching enemy. Then he charged, and the enemy abandoned the position and fled.

In a follow-up attack, word was brought to Alexander that the armies of Cleitus and Glaucias were encamped not far away, without fortifications or sentries; striking quickly, and again in darkness, he took the Guards, the archers, and infantry troops across the river to make a surprise assault, which was totally unexpected and totally successful. The complete campaign to confront and smash the Illyrians had taken approximately a week.

The rebellions in the north had been quickly and decisively quelled in a matter of three months. More importantly, elements shown in these early battles would reappear again and again in Alexander's future - his ability to quickly out-think unexpected threats; to extract his army from difficult terrain; to arrange his supply-lines and to think ahead to coordinate with other forces; his use of night manouvers to rapidly move troops into position to surprise the enemy; his use of psychological intimidation such as putting his troops through difficult drill to frighten his enemy; his remarkable speed of movement; and his constant ability to change his plans to accommodate the current tactical situation or topography of battle.

Perhaps most importantly, in the very dawn of his military career, Alexander showed that he could flexibly deal with guerrilla attacks; by far the majority of the actions he would fight in Asia would be of this nature, rather than set-piece battles. Like all great commanders, his actions north of Macedon prefigured the qualities that would make him a military legend in Persia.