With Scythia minor firmly under Roman control, Caesar assembled his forces and marched onward, while leaving behind the Legio VIII to reinforce their rear in Scythia minor, including dredging out sections of the Danuvius and building an intricate system of dikes and levies to allow for the flooding of the marshlands, in case of Dacian attacks.
Caesar led the main body of his forces up, along the Hierasus (Siret) River, towards the Dacian city of Petrodava, while his lieutenant, Lucius Octavius, lead the Legio X up the coast, to take the port of Tyras, near the mouth of the river of the same name (Dniester). Caesar planned to isolate the Dacians from their chief allies, the Bastarnae, with this phase of the campaign.
Octavius had little difficulty in securing Tyras, surprising the Dacian force assigned to defend it. He quickly set about reinforcing the defenses of the city, which soon proved necessary, as the Bastarnae army bore down on his position, besieging the city after an initial attempt to storm the walls proved unsuccessful.
Meanwhile, Caesar was faced with the main body of Burebista's army, under the Dacian king's command. Caesar had, in his army, three legions and their auxiliaries, totaling roughly 48,000 men, as well as 10,000 Thracians. Meanwhile, Burebista had over 100,000 soldiers in his army, hoping to crush Caesar's main force in a climactic battle. The two armies clashed south of Proboridava, where a tactically inconclusive battle took place, with moderate casualties on both sides.
However, Burebista's plan was to hold down Caesar's forces long enough for the Dacian force to circle around them, cutting off their access to the lower part of the river. The inconclusive bloody battle served this end perfectly, especially since Burebista's larger force could weather casualties with less difficulty. By the end of the battle, the Romans were faced with a Dacian army both to their north and south, preventing them from advancing either further along the river or back to their base of operations, at Barbosi. Caesar, surmising the Dacian strategy, conducted a forced march eastward, to the next branch of the Hierasus river, continuing his march up that branch.
Burebista then sent a smaller contingent of his army after Caesar, to follow him up the river, while his main force continued back up the main branch of the Hierasus, assuming that Caesar intended to circle around the Dacian forces and resume their advance on Petrodava. However, several days into the new march, after some distance had been placed between Caesar's army and his pursuers, and the main Dacian force, the Roman army spun around and engaged the pursuing force.
The resulting battle went quickly in the Romans' favor, as the Dacians were not prepared for the onslaught. Caesar made special effort to annihilate the army, before turning eastward, and marching in relief of Octavius at Tyras, where more and more of the Bastarnae were gathering and constructing ships in order to starve the city into submission.
As Caesar's army arrived at Tyras, the Bastarnae began to abandon their efforts of the siege and focus on repelling the new army. The main Bastarnae force, under the command of their king, Zanatis, attacked the Roman troops relentlessly and savagely, their cavalry more than a match for the Romans, thus enabling the barbarians to press the Roman force on two different flanks. As he saw his lines buckling and breaking, Caesar rushed to the front and began shouting to individual centurions and encouraging them, heading into the heat of battle itself.
The legionaries, seeing their general rush off into battle as they were being beaten back, hardened their resolve and stood firm. Still, however, the Bastarnae continue to hammer into them, bloodying their army. Caesar's bravery (or recklessness) again proved to be decisive. As he fought the enemy, he came into battle with Zanatis, their king, himself. The two fought for some time, until Caesar slipped on the blood drenched ground. Zanatis then thrust down his sword powerfully at the Roman general, who was able to roll out of the way just in time, the blade sliding along the side of his armor. Zanatis himself was caught off balance by his thrust, and Caesar thrust his gladius into the king's stomach, killing him and earning Caesar the Spolia Opima, the highest award any Roman could ever receive, which had been verifiably awarded only once before (though two, including Romulus, had received it in legend).
The soldiers on each side around them had become somewhat transfixed on the battle, and the Bastarnae were disheartened, while the Romans were encouraged. These feelings soon spilled throughout the lines, and the Romans redoubled their efforts, while many Bastarnae fled in distress. What looked to be a possible defeat for the Romans soon turned into a clear victory, as the Bastarnae army was shattered and demoralized.
After the battle, a delegation of Bastarnae nobles came forth to seek peace with the Romans. They honored Caesar with many gifts for his bravery, and pledged that they would not seek war with Rome any longer. Caesar accepted their peace offer and negotiated an alliance with the nobles, thus shoring up the northern front of the war. The assembled parties agreed upon the border between Rome and the Bastarnae to be the Tyras river
By this point, Burebista was facing reports of increasing attacks from the Roman allies, the Jazyges, in his western realms. Confident in the impregnability of the fortified cities of Dacia, he gathered the bulk of his forces and led them west to battle the Jazyges. Thus, as Caesar's forces began to march into the Dacian heartland, Burebista was battling the Jazyges.
The records of these battles are not as detailed as those directly involving significant Roman forces, but the outcome is clear. After a series of major battles, the first being fought in the mountain passes near Tapae, the Dacians were able to defeat the Jazyges and subdue them. The final battle of this campaign was during the winter of 696-7 AUC (58-7 BC), when the Dacians launched a surprise attack over the Tisia (Tisza) river, catching the Jazyges off guard. Subsequently, the Jazyges swore their allegiance to Burebista, effectively reversing the major alliances of the conflict.
As the winter set in, with the Romans laying siege to the eastern cities of Dacia, Burebista had a new plan for the war. He intended allow Caesar to invest himself in long, protected sieges, while he would continually harass the Roman forces apart from the main army, wearing them down until he could crush them. Meanwhile, Caesar was busy shoring up his supply lines and expanding his forces, reinforcing his current legions and recruiting a sixth legion, the XIV Falxa (named after the Dacian curved sword, the Falx), which contained a significant proportion of natives.
And so Caesar's war in Dacia continues. I've been torn about the writing of this segment. On the one hand, Caesar clearly is going to win, given the theme of this history, and the fact that he's a really good general with a really good army. On the other hand, I don't want to make it too easy on him.
I also decided that Caesar should get the award of Spolia Opima, given to a Roman general who defeats the opposing commander in single combat. Before him, only three Romans ever achieved the honor, making it the highest award any could receive. Those three were Romulus, Aulus Cornleius Cossus, and Marcus Claudius Marcellus (one of Rome's best generals, ever). Of those, only Marcellus is verifiable. In our history, no other Roman would ever receive Spolia Opima. There was the case of Marcus Licinius Crassus (grandson of the triumvir of the same name), who defeated the king of the Bastarnae in combat (the inspiration of this segment). However, Augustus denied him the award on a technicality, as Augustus was, in theory, the Roman commander, by merit of his political position.
Also, a note about the Jazyges. They're known more commonly in our history as the Iazyges, but I decided to translate them with a 'j' instead of an 'i', as that is an accepted spelling, and, since I haven't been spelling Julius as Iulius, it seemed only fitting.
Lastly, Octavius is the brother of Gaius Octavius, the father of Augustus. I originally intended for Gaius Octavius himself to the commander, but decided that he was too much Caesar's peer to be serving under him (they were roughly the same age and Octavius even advanced quicker up the political ladder, in our history). Instead, I decided that a younger brother of Octavius would serve the same purpose quite nicely.