Prelude
After losing two field armies to the Aureans in the disaster at Jamukha's Ford, the Tangolian Khan Qajeer spiraled into escalating fits of madness that left him incapacitated for the rest of the war. His eldest son Hulegu was made regent and promptly took control of the rapidly deteriorating situation. Knowing that at this point it was too late for the Tangolians to win the war outright, he retooled the Tangolian strategy to focus more on prolonging the conflict as long as possible, using guerilla tactics in areas under Aurean control, and winning battlefield victories, hoping to lower Aurean morale to the point where the Aurean public would demand their leaders sign an armistice recognizing Tangolian independence. Nevertheless, almost as soon as Hulegu took power, the Tangolians suffered another massive setback when two Aurean field armies under the command of Zoe Laskaris landed on the east coast, annihilated the three field armies defending it, and pushed inland to Uihae. While Laskaris was wintering in Uihae and the other Aurean commanders were busy discussing strategy in the capital, Hulegu used the time to raise four new field armies: two for staving off the imminent Aurean attack from his west, and the other two for dealing with Laskaris to the east.
Secondly, Hulegu replaced many of the inept commanders his father had put in charge, most of whom were his friends or important nobles, with people he trusted and had proved themselves on the battlefield. Khosbayar Arslan, who had been killed at the Battle of Jamukha's Ford, was replaced with his much more capable son Khosbayar Arslan II, who had devised the strategy Qajeer used to annihilate three Aurean field armies at the Battle of Ascrus. Fiyanggu Wilan, who had been captured at the Battle of Jamukha's Ford, was replaced with Tashhira Akhtar, who had given Laskaris's forces trouble at the Battle of Weh Astras Khusrau. Demirgian Kipchak, who had been killed at Jamukha's Ford, was replaced by Evin Memis, a lower-ranking officer who had given even the great Taftus a run for his money at the Battle of Zhaoramay.
Hulegu would take Arslan and Akhtar west with him to wait for the attack there, while Memis was sent east to intercept Laskaris. Laskaris ended up moving first, hoping to surprise the Tangolians by sailing down the Ferum-Hsia River to Otrar in the middle of winter and taking that crucial fortress without a fight. However, Memis was warned of her approach by scouts, and crushed her at the Battle of Otrar, forcing her to retreat to Uihae with only half the forces she started with. This victory saved Tangolian morale from utter collapse at a crucial point and made the Aurean public begin to question whether their leadership could beat the reorganized Tangolians. Memis then pursued Laskaris northeast to Uihae in hope of retaking it. While Memis's assault on the city did not go well, she nevertheless was able to surround the city and settled in for a siege.
Meanwhile, the Aurean high command bickered in the capital about when and how a strike on the Tangolian heartland from the west would be done. They agreed that they would go in with the same two field armies that won the Battle of Jamukha's Ford, albeit with more crossbowmen and much more cavalry to help deal with the problems they faced with Tangolian horse archers during that battle. However, Pompeia Khan, the Domina and Head of State, and Taftus, the Magister Militum and mastermind of Jamukha's Ford, bickered endlessly over who would command what. Taftus wanted Andreas Pavlou, their political rival who constantly undermined him and Pompeia politically in his newspaper The Free Aurean, removed from command before he could cause more problems, but Pompeia forced him to keep him on due to removing him being politically untenable after his heroism at Jamukha's Ford. Almost all the rest of Taftus's old Legates were allowed to stay on as well, with the exception of Gaius Martinus Theodosius and Fabia Tucciana, who were sent to oversee the occupation of Tangolia's west coast. Theodosius and Tucciana were replaced with Dihya and Lucius Sempronius Pastor respectively, Dihya being the Exarch of Tifinagh and a talented cavalry commander, and Pastor being Pompeia's Consigliere (essentially chief advisor, second-in-command, and heir should she die in office). Gorgo Gualtera, Pompeia's Magister Equitum (supreme cavalry commander) filled in for Antonia Virginiana, one of Taftus's Legates who was killed at Jamukha's Ford.
While Taftus's units were all replenished to full strength after the somewhat heavy casualties his infantry took at Jamukha's Ford, many of the new recruits that filled these holes were newly emancipated servi agri (serfs whose status Tangolia had revolted over in the first place and who the army had recently been given permission and orders to free from bondage by Pompeia Khan's Tangolian Freedom Act) who had been hastily trained in only a few months, were universally uneducated and illiterate, and only spoke Tangolian languages, meaning only ethnically Tangolian officers could lead them. As a result, much of the invasion force was uncharacteristically green for the normally professional Aurean military, and many lower-tier officers serving under Taftus's Legates had to be replaced with ethnic Tangolians from other units. This led to numerous accusations from Pompeia's political rivals and the press that she was "Tangolianizing" the army, which tapped into extensive anti-Tangolian racism in Aurean society, especially a problem for Pompeia due to her being half Tangolian herself. However, despite their relative lack of training, former servi agri were said to be quick learners, and as they were fighting for their freedom, they had the highest morale of any soldiers in the entire Aurean military.
The only thing all these commanders agreed upon fairly quickly was that the invasion, which would come to be known as the River Campaign, would gather at the city of Ferum in Argentolia, sail down the Arax and Ferum Rivers to the Tangolian border, take key forts and ports along the river like Bost, Dörtyol, Kavusabad, and Sumqayit, and advance to the Tangolian Capital at Tengribalik. Meanwhile, a smaller force under General Leonidas Dukakis would sail down the less defended Hsia River to the north and take the key fortress of Rishud.
However, they could not agree on when to launch the campaign. Pompeia wanted to begin as soon as possible, having experienced many under her command dying of heatstroke in the desert leading up to the Battle of Ascrus, which took place during summer. She knew that the desert temperatures would be much milder during the winter. Also, she knew that farms and towns in the area would still have at least some stored food left during the winter the army could take while foraging. Additionally, Pompeia needed a quick victory to secure reelection, which was coming up in the summer and she could not risk this campaign dragging out beyond that, especially since she needed a victory soon to distract the public from her administration's recent scandals. Taftus, on the other hand, wanted to wait until the spring floods, mostly because the river would not be at its full width or depth until then, and attacking before that would give the enemy exposed high ground around the river that would make riverside towns much easier to defend. He also argued that the nature of the River Campaign would allow them to easily resupply as they went via river boats, so extensive foraging would likely not be necessary. Eventually, Pompeia's plan won out and it was decided that they would set sail from Ferum on New Year's Day, 2 AR, and its first landing would be to secure the town of Bost, an important port and rail hub on the south bank of the Ferum River, just over the Tangolian border.
While Hulegu correctly guessed that the attack would come in winter for political reasons, he did not know at first whether the main attack would be along the Ferum River or the Hsia River. While he knew if the Aureans attacked along the Hsia River that they would have a much easier time neutralizing Rishud and clearing the path to Tengribalik, he also knew that the banks of the Ferum River were much more developed and had more ports for the Aureans to resupply at. However, details of the Aureans' plans would come to him when a private letter discussing them was intercepted by Tangolian spies and brought to him.
Hulegu swiftly moved his force to Bost to await the Aureans. The town sat on the south bank of the Ferum River, with a both a road bridge and a rail bridge crossing the river into the city immediately parallel to each other. As this was the dry season, the river was not its full size, with hundreds of feet of riverbed on each bank exposed. Bost sat just where the ground began to slope down into the riverbed, as this would be the riverbank during the spring floods when the river would be at its full size. The town had two sets of docks: the "high docks", which were only usable during the wet season, stretched from the town out into the air above the exposed riverbed. The "low docks", which were used during the dry season, were located where the currently exposed riverbed met the Ferum River, and would be underwater during the wet season. Knowing that when he arrived at the town, Taftus would have to disembark on the low docks, Hulegu saw an opportunity to turn the exposed riverbed, which would later come to be known as "the Bloody Banks", into an Aurean killing field: he split his asker heavy infantry into three groups, each defending one of the three areas where the slope of the Bloody Banks was gentle enough for Aurean troops to scale it. One was to the north of the town and closest to the docks, which would be commanded by Arslan; the second, roughly in the center of the area and just south of the town, would be commanded by Hulegu himself; and the third, just southeast of Hulegu, was commanded by Akhtar. All along the line, his crossbowmen were positioned thinly just behind his infantry to rain arrows on the Aureans as they would try to climb out of the Bloody Banks. His horse archers were split into two groups: one on the Bloody Banks just far enough northwest to be out of sight, and the other just far enough southeast on the Bloody Banks to be out of sight. His elite Spahi heavy cavalry, commanded by Kim Seo-Jun, was kept as a reserve force just south of the town.
Further to the south of the town was a crescent of somewhat high ground: the steep Smithy Ridge just a few hundred yards south of the town, as well as the more gently sloping Öz's Hill to the ridge's southwest, and the also more gently sloping Bozkurt's Hill to the ridge's southeast. Hulegu decided to fortify this area as a backup position should the Aureans manage to overrun him.
Battle
At 7 AM on January 15th, 2 AR, Taftus and Pompeia prepared to land their field armies at Bost's low docks, still thinking they had the element of surprise and not expecting resistance. As a result, they were taken completely by surprise when the first of their boats suddenly found itself under a hail of arrows from Tangolian crossbowmen as it neared the docks. Caught completely on the back foot and forced to improvise, Taftus ordered all his legionnaires and crossbowmen to disembark first, with his legionnaires in testudo formation to minimize deaths by arrow and with the crossbowmen on the flanks facing out, with a single line of legionnaires in front of the crossbowmen. This was to defend against any Tangolian attempt to flank them with cavalry while they were vulnerable. While Taftus managed to stay calm enough under pressure to get all his infantry and crossbowmen disembarked this way, the casualties during this phase of the battle were extreme, with wave after wave of arrows causing thousands of serious wounds and deaths as the troops landed at the lower docks. One of Taftus's Legates, Sextus Cornelius Aquila, was killed by an arrow to the eye barely twenty minutes into the fighting. Taftus's cavalry, who lacked shields to defend against the arrows, was left on the boats for the time being for their own protection. Almost as soon as Taftus finished disembarking his infantry, Tangolian horse archers appeared from each of his flanks, racing in from the positions Hulegu had put them in prior to battle and peppering Taftus with their usual hit-and-run tactics. This is where Taftus correctly guessing Hulegu's strategy saved him, as the outward-facing crossbowmen and single line of legionnaires he had put on his flanks was enough to both stop them from doing much real damage and drive them away with heavy casualties whenever they appeared.
Once Taftus had enough breathing room from the horse archers to form proper lines, he organized his troops into a horseshoe surrounding the low docks, with the river to his back. The mixed crossbowmen-legionnaire formations were reorganized into the horseshoe's flanks, still facing outward to intercept any further actions by the horse archers. Taftus immediately conferred with the other commanders, as he had found himself in the situation he feared most in his entire career: caught in an enemy ambush with no idea how many troops they had, which kinds, or where all of them were located. All the commanders present knew that regardless of where the rest of Hulegu's forces were, the only way out of this situation was up, but none could agree on where the best place to attack Hulegu and escape the Bloody Banks was. They were able to see that Hulegu had concentrated his forces in three areas: one in the northwest, one in the center, and one in the southeast, but none had any idea which of these potential targets was softest. Pavlou pitched the idea of breaking their force into three groups to mirror the Tangolians and attacking each of the three enemy groups simultaneously while the crossbowmen provided covering fire, but Taftus and Pompeia shot this down because having the crossbowmen switch to firing up the Bloody Banks would leave their flanks exposed to further interference from the horse archers. Dihya pitched the idea of concentrating their forces on the north, breaking through there, and then moving southeast to roll up their left flank. Taftus and Pompeia liked this idea somewhat better, as the two bridges into the town would provide cover from the enemy crossbowmen in the center and southeast, but Taftus had a feeling that Hulegu had planned for this and had a reserve of some sort waiting for them behind the Tangolian lines.
Finally, Pompeia pitched the idea of concentrating on the enemy center, either breaking through it and allowing the Aureans to scale the Bloody Banks, engage the Tangolian left and right separately, and defeat them in detail; or forcing the Tangolians to pull troops from their left and their right to reinforce their center, allowing Gorgo, who was still on the boats with the cavalry, to disembark, split her forces, and then have one half smash the weakened Tangolian left and the other smash the right. Additionally, Pastor noticed that the bridges would provide cover from enemy arrowfire from the north, and the angle of the Bloody Banks made it somewhat difficult for the crossbowmen on the Tangolian south to hit an Aurean attack on the center. It was then decided that this was the plan they would go with, and the Aureans began marching up the Bloody Banks towards the Tangolian center.
While Hulegu had anticipated the Aureans would likely go for his north, he was still unperturbed by this, as unbeknownst to the Aureans, his Spahi reserve was located just behind his center and he could easily use this to push them back down the hill if they started breaking through. While the Aureans did manage to reach the top of the Bloody Banks, casualties rapidly mounted from arrowfire as they climbed the hill, even with many of the Aureans' own crossbowmen providing covering fire. This was in part because Taftus still refused to commit all of the Aureans' crossbowmen to this out of the fear that the horse archers would return and flank them. While the Aurean legionnaires had superior discipline and morale to the Tangolian askers, they were largely unable to bring their superior numbers to bear due to the choke point created by the steep slopes, resulting in the Aureans suffering disproportionate casualties. By around noon, however, the Aureans had managed to push the Tangolian center back, finally escaping the Bloody Banks. However, this is just what Hulegu was counting on, and as soon as the Aureans were over the top, he ordered Kim Seo-Jun and his Spahi to come out from behind the town and charge the Aureans' right flank.
While the crossbowmen Taftus insisted on keeping in reserve on their flanks mitigated the damage, the Aureans were driven back with heavy casualties, and in concert with Hulegu himself rallying his center into a counterattack, the Aureans were driven back down the Bloody Banks back to where they started. After this setback, one of Taftus's Legates named Numerius Julius Tyranus floated the idea of disengaging, going back to their boats, sailing to the next town, and redeploying there, but Taftus explained to him that since the Tangolians held the high ground along the river, they would be able to see everything and would just beat them to the next town, reiterating that this is why he wanted to wait to do this until the spring, when the river was full and there was no exposed riverbed. Taftus also added that despite the setback, since they had briefly reached the top of the Bloody Banks, they were able to see the full extent of Hulegu's defenses and he then had a much better idea of what they were up against.
Just as Taftus was about to unveil his new plan, however, the horse archers, on Hulegu's orders, ambushed the Aureans' makeshift camp from both flanks. While Taftus was quickly able to scrape together his mixed crossbowmen-legionnaire formations to prevent a complete disaster, Tyranus was shot in the neck with an horse archer's arrow while rallying one of these formations, killing him. Needing the horse archers gone to have any chance of winning the battle, Taftus had no choice but to order Gorgo off the boats and to charge the horse archers. The horse archers were caught by surprise between the Aurean lines and Gorgo's cavalry and were decisively routed from the field as a result, but Hulegu had successfully forced Taftus to reveal the last card he had left in his hand by doing so.
With his cavalry revealed and their element of surprise gone, Taftus had to come up with a new plan and fast. For once, he and his generals found themselves in unanimous agreement on what to do next: their last option was simply speed. Before the Tangolians could fully fortify their northwest and southeast positions, Gorgo would split her force and charge each of them while she still can. Meanwhile, Aurean infantry, with full covering fire from their crossbowmen, would attack the weakened Tangolian center and push them back. After breaking through the Tangolian northwest and southeast, Gorgo would flank the Spahi reserve from the west and east, annihilating it, while the Tangolians retreat to their prepared fortifications on the hills south of the town. While Hulegu was busy defending these fortifications, Gorgo's cavalry would race around them before he could react and attack his rear, trapping him and forcing him to surrender.
At around 2:00 PM, the plan was put into action. The first part of the plan went as well as possible for the Aureans, with the Aurean infantry successfully pushing back the Tangolian center and Gorgo's cavalry successfully pushing the Tangolian northwest and southeast back from their positions, finally escaping the Bloody Banks. However, Hulegu withdrew his Spahi before Gorgo could wheel around and ensnare them, instead redeploying them to guard his fortifications' rear as his infantry and crossbowmen retreated to their fortifications atop the hills south of the town. While the Aureans had escaped the worst part of the battle, Hulegu was still in a very good defensive position and the Aureans had suffered just as many if not more casualties in their final push up the Bloody Banks as the Tangolians did. Nevertheless, the Aureans had taken the town of Bost and camped within it for the night.
Hulegu convened with his subordinates that night and they more-or-less unanimously agreed that their best bet would be to hold their current position, pepper the Aureans with arrows from it constantly to remind them that they could not hold Bost without taking the fortifications, and wait for them to retreat. Kim Seo-Jun's Spahi would continue protecting the exposed, flat rear of their position from any attempts by Gorgo's cavalry to encircle them. Arslan would command the Tangolian left on Öz's Hill, Hulegu himself would lead the Tangolian center on Smithy Ridge, and Akhtar would lead the Tangolian right on Bozkurt's Hill.
The next morning, the Aureans deployed for battle in lines more-or-less mirroring those of the Tangolians. Taftus and Pompeia jointly commanded the Aurean center, joined by Pavlou. The Aurean right would be commanded by Taftus's Legates Karadağ İngie and Tiberius Constantinus Augustus, joined by Lucius Gallus Pastor. The Aurean left would be commanded by Legate Chyrsanthe Exarchopoulos, alongside Dihya, the latter of which would be in command of two legions instead of one due to Tyranus's death. Finally, Gorgo Gualtera would command the Aurean cavalry, who would wheel around the fortifications and try to break through Kim Seo-Jun's Spahi. While the Tangolian center was by far the weakest part of their army, Taftus and Pompeia dared not attack it, at least not yet, as the front of Smithy Ridge was steep enough to make a direct frontal assault suicide. Instead, they ordered simultaneous attacks by each of their wings on the Tangolian left and right, knowing Hulegu could not further weaken his already weak center to reinforce them. The Aurean right's attack on Öz's Hill went fairly well, with Pastor's legion managing to get into the low saddle between Öz's Hill and Smithy Ridge, push the force guarding it back, and even attack into Arslan's rear briefly before being pushed back by some Spahi Kim Seo-Jun detached from his main force to repel them. However, chaos ensued on the Aurean left, as Dihya found herself in command of many of the former servi agri despite barely speaking a word of Otrar Tangolian, as opposed to Tyranus, who was fluent (although not a native speaker). As a result, she had to relay of her orders through the ethnically Tangolian centurions who served under her, and because they were used to Tyranus, who they liked, instead of her, much of what she told them was either disregarded, interpreted incorrectly, or lost in translation. As a result, instead of launching massed attacks into the low saddle between Bozkurt's Hill and Smithy Ridge to mirror what Pastor had done, Dihya's legion made limited, scattered attacks on the steepest part of the hill, all of which were bloodily repulsed. Despite successfully defending her lines, however, Akhtar was killed towards the end of the second day's fighting by a former servi agri in Dihya's legion named Fereydoun Aydin, who was able to identify her because she had been his former master. As this was happening, Gorgo split her cavalry again and attacked Kim Seo-Jun on each flank, significantly weakening him but not by enough to break through. This continued for the rest of the day until both sides returned to their camps for the night.
With his left and Spahi significantly weakened by Pastor and Gorgo's assaults, in addition to his center already being paper-thin after the fighting on the first day of battle and having lost Akhtar, Hulegu realized the situation was untenable and decided to disengage before Gorgo could defeat Kim and cut off his retreat. That night, Hulegu and the remainder of his forces fled the battlefield under cover of darkness, escaping via the road heading to the south.
Aftermath
Although the Aureans had technically won the battle, this showed Hulegu would be a far tougher nut to crack than his father or the inept commanders that served under the latter. The Aureans, who hadn't even planned on fighting a battle to take Bost, suffered 21,000 killed, wounded, or missing here, nearly double the 11,500 killed, wounded, or missing the Tangolians had suffered during this battle. This was despite the Aureans outnumbering the Tangolians 95,000 to 60,000 at the start of the battle. On top of this, Hulegu had slipped through Taftus and Pompeia's fingers, evading capture or death unlike the other Tangolian generals they had gone up against so far. The vast majority of Aurean casualties had been on the first day of battle, suffering 1,500 deaths in the first three hours of fighting alone. Predictably, Pavlou immediately began writing editorials in The Free Aurean criticizing Pompeia and Taftus's generalship during the battle, referring to them as "inept butchers" who kept getting their soldiers killed with reckless assaults, insisting he would have lost far fewer troops had he been in supreme command. In his anti-Tangolian racism, he even lied about Akhtar's death, claiming she was killed by a stray arrow rather than by her own former servi agri who had been fighting in the Aurean army.
In addition to having suffered a nearly 1-in-4 casualty rate, Taftus lost two of his experienced Legates, Tyranus and Aquila. While neither of them were exactly tactical geniuses, Tyranus was a fluent speaker of Otrar Tangolian in an increasingly Tangolian army where officers who actually spoke those languages were a rarity, meaning one of the first things Taftus had to send for after winning the battle, on top of supplies and reinforcements, was a Legate from some other legion who spoke fluent Tangolian and could replace him, as Dihya certainly could not fill the role long-term. The only other Legate in his force who spoke fluent Otrar, Karadağ İngie, who was of Tangolian heritage himself, already commanded a mostly Tangolian legion, and writing to the Aurean Senate to have one of Tyranus's centurions promoted to fill the role would take far too long. This conundrum brought a huge amount of bad press to Pompeia's Tangolian Freedom Act, with her opponents using this to claim that her efforts to recruit former servi agri into the army were undermining the war effort. However, Pompeia was able to stave off the worst effects of this by milking Fereydoun Aydin's heroism and killing of Akhtar for all it was worth.
While on paper, the Tangolians had walked away from this battle in better shape than the Aureans, Hulegu had still lost Akhtar, one of his best commanders, during the battle, and in a way that was particularly embarrassing to his cause. More importantly, while the Aureans had suffered grotesque casualties, the Aureans were easily able to replace their losses, while Hulegu could not. The amount of Tangolia Province actually under his control dwindled by the day, and he was also simply running out of Tangolian nobility to fill his ranks. He was increasingly forced to conscript the very old and the very young, with Pompeia remarking during the battle upon seeing the troops defending the hilltop fortifications, "a soldier lost by them cannot be replaced. They have robbed the cradle and the grave equally to get their present force". Recruiting servi agri was not an option, as doing so would betray the very reason he and his allies were fighting for Tangolian independence: to maintain the servi agri system.
Nevertheless, Hulegu still had a good 50,000 men in his force he could continue to resist the Aureans attacking him to the west with, and Memis was still keeping the other Aurean force to his east under Laskaris on the defensive in the Siege of Uihae. The River Campaign had begun, and if this battle demonstrated anything, it was that it would be a long, miserable, and bloody slog.