Alexander at his operational best

Advance into the Caspian gates

As Alexander was marching with his army to Ecbatana in Media where Darius was with his troops,which numbered 6 to 7000 infantry and 3000 cavalry, it was reported to him that Darius had been promised reinforcements by the Cadusians and the Scythians. Darius remained in Media while sending his women and covered wagons to what are known as the Caspian gates.

Darius's intention was to retreat to the interior by the way of hyrcania and parthia and into Bactria while laying waste to all the places that lay along his path to impede Alexander's advance. He could also hope to gather reinforcements from these places as he passed through with his army.

Upon learning of this report Alexander made all haste for Ecbatana. Leaving the pack animals as well as the baggage behind under the protection of their guards Alexander led the remaining troops in battle order and arrived in Media on the twelfth day. There he learned that no Scythian or Cadusian reinforcements had arrived and that Darius had resolved to flee.

To advance further from media in pursuit of the remnant of the Persian army under Darius Alexander divided his army into two main columns. The one under Alexander's personal command Marched eastwards towards Rhagae and onto the Caspian gates in pursuit of Darius while the second column was put under the command of Parmenio and was ordered to march north and from there to strike northeast,keeping roughly parallel to Alexander's own march,into Cadusia and then to Hyrcania respectively to prevent the Cadusian reinforcements from reaching Darius.

Parmenio's column would also cut off the adjacent satrapies(i.e Mardia and Hyrcania) to the retreating Persians in case they directed their march to these places in hopes of supplying themselves and raising new levies to bolster their army or go on the offensive in Alexander's rear much like the remnant of the Persian army post issos who attempted to threaten Alexander's rear communication by levying troops from places like paphlagonia.

(ONE OF THE FOREMOST MODERN AUTHORITIES ON ALEXANDER A.B BOSWORTH IS OF THE VIEW THAT THIS ORDER WAS LATER COUNTERMANDED BUT I PERSONALLY WOULD SETTLE FOR A COMPROMISE THAT PARMENIO MADE IT AS FAR AS CADUSIA SINCE ALEXANDER TURNED AGAINST HYRCANIA AND MARDIA TO SUBDUE THEM BUT NOT CADUSIA THAT LIES DIRECTLY NEXT TO MARDIA AND HAD EVEN PROMISED REINFORCEMENTS FOR DARIUS AND WERE A HOSTILE THREAT.)

keeping the above consideration in mind if parmenio actually managed to advance beyond Cadusia then The column under parmenio would cover the left flank for Alexander during the latter's march from where he intended to march into Parthia. There he was to make a junction with the troops left in Ecbatana by instructing Clietus, who was left in Susa, to take control over them upon reaching Ecbatana and go into the direction of Parthia and link up with Alexander.

When Alexander reached a place which was only a few days' march from the Caspian gates he learned that Darius had already passed through. Alexander gave up on his pursuit and encamped at this spot and sent koinos son of polemacrates to forage for supplies since the land beyond was uncultivated. Some Persian deserters from Darius's camp came to Alexander and informed him that Darius had been overthrown in a coup led by Nabarzanes the commander of the King's royal squadron and Bessus the satrap of Bactria.

On the strength of this report Alexander immediately set out with his picked body of troops while leaving krateros behind with the rest of the army to follow. After some forced marches Alexander finally reached the place where the enemy had bivouacked the night before.

Here Alexander inquired with the locals if they knew a shorter route through which he could catch up to Bessus.They said there was but it ran through a waterless and uninhabited country. Despite this Alexander asked them to act as guides and began preparations to march through this desert track(More or less to the south of the Caspian gates while to its north it is bordered by the Elbruz mountains). Alexander knew he couldn't catch up to the enemy by moving his full force so he devised a bold plan of operation.

For the march through this waterless region Alexander selected the cavalry and 500 mounted infantry and took with him provisions for 2 days while leaving the rest of the army,divided into two parts with the advance guards equipped lightly as possible to increase their speed,with the instruction to tail the enemy by marching along the path taken by Bessus in order to keep the enemy constantly on the march so as to to attrite them,who by this point would have likely been worn out by the constant marches from the preceding days, and give them no opportunity for respite lest they be overtaken by the large Macedonian column following behind.

With the two Macedonian columns closely following on the Enemy’s heels Alexander must have hoped to herd Bessus(The last thing the fugitives would have expected was a flying column to suddenly spring out from the land adjacent to their line of march) into straying right towards Alexander's detachment while Bessus was trying to evade the two Macedonian columns in his rear.

Meanwhile Alexander temporarily cut loose of his communication and marched via the waterless route with nothing but 2 days ration and weapons to lighten his troops as much as possible and to increase the speed of their march knowing that the enemy would be marching with their baggage and the camp followers. Marching outside the route taken by the enemy Alexander first cut through this shorter albeit difficult desert track before curving back towards the main road,through which Bessus was retreating, from a different axis of march.

In the haste to get clear away from the Macedonians following behind Bessus was thrown right into Alexander's advancing column before dawn. Alexander came upon them when they were still in the order of march and were found unarmed, likely due to them having just broken camp,and straggling(may be implying that the enemy were strung out in their march) along the road without proper order. My personal conjecture is that many of the enemy troops were fanned out in their foraging expeditions or to collect woods and so when Alexander struck they quickly dispersed which might explain why Bessus made his escape with only a few hundred horsemen. Bessus with a handful of men fled east towards Bactria.

At this juncture the remaining troops made junction with Alexander. Sometime earlier Alexander had received a report about the Grecian mercenaries, who had accompanied Darius in his retreat,escaping to the mountains of Tapuria in Hyrcania which lay roughly to the northwest of Alexander's position.

Alexander successfully interposed himself between the two disjointed wings of the enemy split in opposite directions.

Alexander first rendezvoused to Hyracania (where Parmenio had sometime earlier set out as per Alexander's order) to the west against the mercenaries. His approach from the east would therefore have likely been supplemented by Parmenio's own expedition directed towards Hyrcania from the west.

Even if Alexander's march to Hyrcania was not synchronized with Parmenio's to a tee the latter lay immediately to the west and thus the mercenaries would have found themselves surrounded from both directions.

Upon his arrival Alexander further divided his column into three to fully traverse the country leaving the mercenaries no room to hide. The Mercenaries soon capitulated.

Alexander then turned towards the Mardians to the left of Hyrcania to subdue the locals and safeguard his rear communication. After accomplishing this Alexander pivoted east against Bessus.

Crossing of the Hindu kush

Marching by the way of Parthia, Alexander reached Aeria(roughly corresponding to the modern heart in western Afghanistan)which borders Parthia to its east. There after letting satibazanes retain his office Alexander continued on his pursuit of Bessus in Bactra (Approximately modern Balkh in Northern Afghanistan),who by now had raised a moderate force consisting of the Persians, bactrians,sogdians,and the scythians.

On his way to Drangiana it was reported to him that satibazanes had revolted and the men he had left behind as a garrison had been all murdered. Satibazanes had decided on raising fresh levies from his province and upon deducing that Alexander had passed through his satrapy he intended to assist Bessus in attacking the Macedonians whenever possible.

Leaving the rest of his forces under krateros Alexander took with him a select body of troops and struck Aeria before satibazanes’s depositions were completed and before he could reinforce bessus. After this brief delay Alexander resumed his march and reached Arachosia(Approximately modern Kandahar in southern Afghanistan). Around this time the infamous philotas affair was uncovered that led to the execution of philotas and his father parmenio on the flimsiest grounds. Parmenio unequivocally had no involvement in the conspiracy. Unfortunately for him his fate was sealed and he was assassinated in Ecbatana. Parmenio was popular among his troops and was a capable and trusted subordinate. His execution was the most unfortunate.

Here, the report reached him that satibazanes had re-entered aeria after being reinforced with 2000 bactrians provided by Bessus and was stirring the people to revolt once more. (An individual by the name of barzanes shows up in arrian's account as the man who was appointed the viceroy of parthia by bessus. His identity has long been a subject of debate with some identifying him as Nabarzanes while A.b bosworth's verdict is that this was a completely different individual who was dispatched by Bessus to threaten Alexander’s rear. I personally subscribe to Bosworth's view. Arrian in earlier text doesn't refer to Nabarzanes as barzanes nor are we told of any sort of redistribution of the satrapies. The satrap of parthia under Darius and later under Alexander was phratapharnes.) This was exacerbated by Bessus sending a certain barzanes to Parthia in a maneuver to the rear, most likely via the northern corridor, with the order to carry on the war as far as Ecbatana in Media.

To secure his western flank Alexander despatched a Macedonian detachment under erigyus and caranus to aeria with the further instruction to Phrataphernes,the satrap of Parthia, to simultaneously join in on the attack against satibazanes from the west while the Macedonian column closed in from the south via Drangiana towards aeria in a concentric operation. However with the approach of barzanes to Parthia pratapharnes was likely tied in his own province and unable to join the attack against satibazanes.

Here the main objective of this Macedonian column was to reopen Alexander's rear communications and prevent satibazanes from overrunning Aeria and possibly linking up with barzanes. Meanwhile Bessus had begun scorching all the surrounding regions in and around Bactria to impede Alexander's advance while to his east the imposing Hindu Kush formed a natural barrier.

In Aeria the forces of satibazanes and erigyus for a long time fought an inconclusive battle until satibazanes was killed in a hand to hand fight after which the rest of the bactrians soon scattered. After securing Aeria the Macedonian detachment was able to drive a wedge between barzanes and bessus.

From Arachosia Alexander veered off further east no doubt induced by the Persians and Bactrians implementing the scorched Earth strategy in places around Bactria. To combat this Alexander decided on misdirecting the enemy by turning his march eastwards only to then make a detour through the mountains in order to threaten bactria itself from an unexpected direction. Once the Bactrians faced the threat of being cut off from their very homes they would be forced into retiring to their own abodes, lest privation begin to set in given that they had already laid waste to all the places around Bactria, turning Bessus's own strategy on its head.

To accomplish this Alexander feigned a march as far as the nearby Indian tribes on the hither side of the Hindu Kush to give the enemy the impression that Alexander was compelled to turn his march towards India due to the enemy employing the scorched Earth strategy.

Upon reaching the foothills of the Hindu Kush, which cuts between what is today Afghanistan and Pakistan, The king made a flank march over the Hindu Kush while using the mountains to screen his movement before debouching into the plains of Bactria. Turning Bessus's left while the enemy were likely split between Bessus with a part of his force in zariaspa, the capital ,and the Persians and Bactrians carrying on with Bessus’s orders around the base of the Hindu Kush.

Alexander's advance to Bactria induced the Bactrians to look out for their own possessions and scatter to their homes.

Furthermore , The Bactrians judged that once Alexander succeeded in overrunning Bactria they would find themselves detached from their own territories as well as their families and consequently would have a hard time procuring provisions due to them having laid waste to all the places in their vicinity. Thus they had a stronger incentive to simply desert for their own interest.

Bessus found himself deprived of his bactrian allies while Alexander was closing on him from the east meanwhile to the west with Aeria once again secured he and Barzanes had no direct communication with one another after the Macedonian detachment under karanos and erigyus interposed itself between the two. Hemmed in from both sides Bessus was left with no other option but to retreat north into Sogdiana with his forces greatly reduced from its initial strength.