While I do reserve the right to change my mind, this plan is that this war is the final Roman-Persian War. They've been near-constant since the beginning of the century, and have been a thing since Crassus was alive, so I think the concept could use a break. That doesn't mean there won't be diplomatic incidents and maybe the odd war scare, but active hostilities won't be a thing after this.
During the OTL 1500s, after the initial Portuguese surge, the new Cape and old Mediterranean trade routes ended up splitting the eastern trade between them. It wasn't until the 1600s and the arrival of the English, French, and especially Dutch in force where the Cape route began to consistently dominate. ITTL, we're seeing more akin to the OTL 1500s situation, where the shift northward, while still present, is weaker.
* * *
Rhomania’s General Crisis, part 5.2-Shooting at Target:
After finishing up its usual autumnal exercises, the Armeniakon tagma does not disperse to its various winter quarters as usual. The bulk heads southeast to Mepsila (Mosul) where its forces are bolstered by various kastron soldiers. After drawing on supplies from the garrison storehouses, the 11,700 strong expedition crosses the frontier.
Surprise isn’t completely total, but close to it. Ottoman spies had noticed the unusual behavior of the Armeniakon tagma after its exercises, as well as small mustering units of reserve kastron forces to forward Roman outposts. But their reports do not precede the invasion by much, and even that potential warning is largely wasted. Launching a Mesopotamian offensive with what is essentially a single reinforced tagma is entirely unprecedented in Roman strategy, so these signals do not register with Ottoman officials.
Another way surprise is upheld is that no formal declaration of war is issued by the Romans until October 5, by which point the Roman expedition is on the frontier. Roman accounts claim they did not cross until after the declaration; Persian ones claim the opposite. Either way, it is not possible for the Roman ambassador in Baghdad to communicate with Strategos Keraunos. His instructions are to deliver the declaration on the morning of October 5; he does not know where the Armeniakon tagma is at that point.
All wars need a justification and the Roman ambassador cites alleged Mesopotamian inability or refusal to control its nomads, who then violate Roman territory. The Romans are thus intervening defensively to secure the area, given Baghdad’s incapacity. This is referring to the frequent nomadic traffic that crosses the frontiers of both empires, as the pastoralists care nothing for such political boundaries; they are focusing on maintaining their herds and shifting from winter to summer pastures and vice versa. Nomads from all sides, Roman, Mesopotamian, Persian, and Georgian (farther east) do this.
There are sometimes feuds and skirmishes, either between various nomad bands or with settled communities. The reasons vary such as from blood feuds or disputes over rights-of-way, but are local in origin and oftentimes nothing more than the commonplace frictions between the nomad and the sown. There is nothing inherently political about any of it, and it has been going on in some form since classical Romans arrived in the east. Only the details have changed. Nor has it gotten particularly more severe of late. In 1660, more Romans were killed because of feuds between Albanian clans than because of this nomadic traffic.
There is more to the ambassador’s message than just this rather paltry diplomatic fig leaf. The ruler of Mesopotamia is Alexandros of Baghdad, the eldest child of Andreas III and Maria of Agra. Out of recognition for his distinguished ancestry, if he surrenders Mesopotamia without a struggle, he will be granted large landholdings in Rhomania and freedom of movement within the Empire. The grants are quite substantial and would make Alexandros one of the greatest private landowners within the Empire. Smaller but still significant offerings are also promised to his mother Maria and his younger brother Nikephoros, who is commander of the Mesopotamian army.
One possible explanation of the offer is that having the children, albeit illegitimate, of Andreas III around would be one way to keep Herakleios III in line, or to act as a possible replacement. The other, and likely more significant, is that this is part of the strategy to take Mesopotamia out quickly, as Mesopotamia is not the real fight. Persia is.
* * *
Topkapi Palace, Baghdad, October 5, 1660:
Alexandros’s chin itched, right at the tip where his brown beard had decided to skip gray and grow a streak of white instead. He clenched his fist, his nails biting into his palms, as he resisted the urge to scratch. It also helped him resist a much stronger urge, which involved a blunt heavy object and the face of the Roman ambassador.
The Roman ambassador, Ioannes Barykephalos, had requested a public audience over two weeks ago, for this specific morning, after receiving a sealed mail packet from Rhomania. That had been a little unusual. Normally such things were scheduled for earliest convenience, rather than a specific date, and a normal ambassador did not get to dictate a normal king’s schedule. The king decided when, or if, he’d receive an ambassador, not the other way around.
But these were not normal circumstances. Although both the Roman and Persian envoys were styled as ambassadors, as if they were posted to a sovereign state, and made requests to his court, Alexandros knew he could not refuse such requests, no matter how irregular. His subservience was made quite clear in the annual ceremony where he signed off half his annual income to the ambassadors, evenly split between them, to send to their governments.
It was somewhat less grating with the Persians. This was Mesopotamia, the old Ottoman heartland, where Osman I, Osman the Great, and his followers had carved out a state for themselves from the fragments of the Il-Khanate. Iskandar, as heir of Osman, had claim to these lands. But Herakleios III had none in Alexandros’s opinion, and there was also his personal grievance with the House of Sideros.
Ioannes had ceased speaking and was now looking at Alexandros, awaiting his response. For a moment Alexandros ignored him, his eyes sweeping across the ranks of courtiers and officials. This was a full court ceremony with everyone in audience. The looks on their faces varied. Some were impassive, not showing what they felt. Those less controlled, or less willing to dissemble, showed a mixture of fear and anger, the proportion varying. Certainly no one looked happy. Alexandros couldn’t look on the face of his mother. She was present, but was behind a screen that hid her from view, in a corner behind him and to his left. This was her usual custom, allowing her to know things and give counsel, but without being too obtrusive and upsetting delicate sensibilities.
He was struggling to think of a polite and diplomatic response when he heard a faint warble and then a long thin whistle come from the screen. It was his mother, signaling him in the aural code they shared along with his little brother Nikephoros. Alexandros looked at Nikephoros, standing next to him at his right hand. Their eyes met, Nikephoros’s glinting, a faint smile on his lips. He too had heard the signal, too faint to be heard by anyone else.
Alexandros looked at the ambassador. “Your master is a liar,” he replied. “And a very bad one at that.” There was a murmur of surprise in the crowd; Ioannes’s expression was blank. “He condemns us for crimes of which he is equally guilty, and he has many crimes unique to himself besides that.
“He offers us great gifts if we should yield to his unrighteous greed, yet why should we believe him? Your master sits upon the throne of our father, enjoying a birthright his family usurped from ours. Your master’s father sought to give us this realm as compensation for that crime, and yet your master, demonstrating not only rampant greed but utter disrespect for the wishes of his own father, seeks to take this realm from us. Doubtless, based on such patterns, in the future he would then seize those gifts you say he will grant now for our obedience, justifying it on claims that have no basis in truth or justice. Your master is a liar and a would-be thief, whose words are false and promises empty.”
“It is regrettable that you feel such emotional grievances against his august majesty, Emperor Herakleios III,” Ioannes replied. “My master has always been a good friend to your Highness and the realm of Mesopotamia. He wishes merely to ensure yours and its wellbeing, its prosperity and security. He offers to take a most heavy burden from yourself and offers great gifts in exchange. Such is the act of a true friend. Surely, your Highness must see that.”
“If your master wishes to show himself a good friend to ourselves and to the people of Mesopotamia, he can easily prove it. He may take his army with which he threatens us with death and destruction and send it back to where it belongs, in his own realm. As for this burden, we neither require nor desire his assistance. His gifts he may keep. We have no need for them, only for him to leave us alone and to abide by the wishes of his father.”
“It is regrettable that you feel that way,” Ioannes said. “But if you do not trust the goodwill of my master, surely you recognize his power, of his vast superiority in arms to your own? Would it not be wiser to submit now, before all the terror and suffering of a hopeless war?”
“The future is never so certain for there to be no hope, and to purchase peace at the price of slavery is a most poor bargain. God alone, the Supreme Judge, upholder of righteousness and truth, the Humbler of the proud, knows the future. He will decide the outcome of the war. We put our trust in him, not in your worthless master.”
Ioannes opened his mouth. “Speak no more,” Alexandros said. “We are weary of this audience and of you. The time for talk is over. You have two hours to vacate the city. If you remain past that time, you will be the first Roman to die for the sake of your master’s greed, but not the last.”
* * *
Riders go out from Baghdad. Some head north, one of them the Roman ambassador and his entourage. Others head south and west, rallying Mesopotamians to the banners, seeking to gather up recruits and weapons and supplies. Still more head east to the court of the Shahanshah, to ask Iskandar to honor the oath he’d made to uphold the legacy of his blood brother, and to bring the might of Persia onto the scales.
To the north, the Armeniakon tagma blasts through the frontier with barely any opposition, but it is soon made clear it will not always be such smooth sailing. The people here have much experience of Roman attacks; their cemeteries attest to that. And the last fruit of Roman military action they had seen were the remnants of the Great Crime, making the stakes absolutely clear in their minds. To this day, no one is sure which village issued the famous response. But one, when summoned to surrender by a Roman cavalry unit, replied “it is plain you wish to exterminate us, and we do not wish to be exterminated.”