...Oh.

It's hard to overstate how terrifying that is. It's not that wyverns or their riders are invincible, and in fact they often take significant casualties in internicine conflicts where there enemies know full well their strengths and weaknesses. But a blow this fast, and this total? It'd be surprising from an apostle, even if perhaps not quite unprecedented. Almost as one, all the riders lucky enough to have a position in the flights further back are going to turn around.

It's not going to be that easy. The first strike was their best effort, at the closest range from the best firing conditions with the most work done to prepare, but they were hardly engaging at the limits of their range either. They can cut a bloody swathe in the retreating riders as well, and where it's not lethal they can injure them enough to make any further fighting very ill advised. Round one against these creatures was bad, and now that round two is going their way they're going to ensure there isn't a round three.

It doesn't get all of them. Lesser or not, they're still dragons, and a clean sweep like the vanguard would take a similar volume of missiles or a lot of collateral damage. Fortunately for the Sadarans, they have neither, and the dath ilani barrage is not enough to kill most of them.

Unfortunately for the Saderans, it doesn't need to. A dragon rider is not a soft target, but almost all of that comes from their aerial maneuverability and the danger inherent in engaging their mount. Their armor is incredibly expensive, but mostly because of how light it is, and the threats it's supposed to war from them are lucky arrows and a near misses from enemy fliers. When pitted against point blank high explosives, it might as well be wrapping paper, and mortal flesh and bone are vastly insufficient to pick up the slack. The wyvern corps entered the battle a wounded beast, and left it a hollow shell of itself, with the now riderless vestiges following their luckiest counterparts back to what is hopefully some measure of safety. 

(Other wyverns scatter across the city, or are too injured to keep flying, or are so driven with rage that they spend enough time hunting whoever hurt them that a second round of missiles can take them down, but wyverns are very exactingly trained and these fill the minority of cases even now).

The person in command when news of the disaster hits the lines is not the Legate. Rank hath it's privileges, and among them in this case is the privilege of getting to sleep during the night in a real bed safely away from the barbarians. That role falls to Tribune Floros, one of the more senior staff officers, and as much as he normally appreciates the trust and honors that come from being a client of one of the Legate's closest allies, he is not prepared to handle this by himself. The wrong word to one of the surviving, battle-shocked aristocrats in the aftermath could see this turn from a barbarian atrocity to an unmitigated blunder, or worse yet an intentional plan by him or the legate, and the outrage that would evoke doesn't bear thinking of. The legate might survive a blow like that, but the same can't be said for him. His family is equestrians, for Deldort's sake - rich and well connected equestrians, certainly, but he doesn't have half a dozen senators and governors as cousins, and his name isn't on any of the earlier successes of this invasion either. So given that he has neither his commander's standing or charisma to help him avert it, he needs help from the man who does.

A runner to wake the legate, double time like you're being chased by hounds, and tell him it's an emergency. The tribune will be making himself busy in a way that doesn't risk contradicting whatever plan Cattaneo decides on. Starting with standing down troops - they weren't going to deploy the army even if things went perfectly, not with everyone settled into their sleep and how hard it would be to coral them back afterwards, but they did have some night-fighting specialist detachments standing by in case the raid was successful enough to make it worthwhile. That's definitely not happening now.

If you're waking him up in the middle of the night for this it had better be important, or so help him-

Well, that'll teach him to tempt fate. 

The legate allows himself a minute to boggle, in the privacy of his quarters. And then a second minute after. None of his first, second, third, or fourth thoughts are the sort of thing he can afford to project right now, and given the situation that trumps even the need for haste. Then he dons the mask of an unflappable general, and gets to work. They're to move the night fighters into the watch rotation, dispersed to prevent any cluster attacks, and when the sun comes up instead of encamping in place they're to head back for the gate. He's moving up the schedule so the legion won't be spending another night on this side, making them resting close to the front lines a needless risk, and he needs the gateway operating at full capacity come tomorrow to get everyone and everything back through quickly. As for the wyverns and their riders, no expense is to be spared on their treatment, including the intercession of his own personal surgeon. Each one that survives is another family he can sew up into helping cast the affair as a heroic struggle rather than a bitter enemy out for a pound of his flesh, at least if he spins it right, and despite the exhaustion his future self will thank him for putting in the effort to meet with everyone in condition for it. 

And someone get a wizard or a priest or a philosopher on figuring out what the fuck just happened to them, and if it's going to wreak similar havoc on the rest of his army tomorrow.

With the amount of surveilance they're doing on the imperials, it's not actually difficult to piece together what's happening, even through the cultural and language barrier. That's not to say that it's completely clear on the details - especially at first, it's not obvious if they plan to withdraw through the portal entirely or just further reduce their radius - but even the deployment of additional troops to the perimeter doesn't dissuade it once they can see where those are being reassigned from. Prediction markets on how much territotory they will control at various future timestamps start trading down quickly, and the estimates of the casualties to accomplish it trend down; the impact on more speculative future markets is smaller, but of course there's movement there too. Their logistics may be subject to bizarre constraints*, but it's not difficult to miss what the changing tempo and movement of resources to and through the gate means for their future, and from what they've seen it would be an expensive bluff to make.

*As with many parts of the invasion organization, the invaders logistics situation is incredibly baffling. It's not merely a question of being primitive, or even of being inconsistently advanced with dath ilani historical techniques, but indeed missing optimization that any eight year old out of civilization ought to be able to manage from a cold start. It's not impossible they're just not that smart, but it seems incompatible with their other achievements, since heritage optimization just isn't that complicated a project compared to the other humanoid variations they've demonstrated.

That leaves them with the question of what to do going forwards. The null action is of course to continue as they were; the plan if it hadn't been interrupted was a night attack of their own, to test if their (hopefully) superior low-light sensory options and ability to shut out the local light sources at will would allow them to get a decisive engagement with few casualties on either side. It's not a bad plan even now, with the updates to account for the changes in invader strategic posture, and on the margins moderately more likely to succeed with enemy air support as a smaller factor. And aggression has a lot going for it as well - if the invaders retreat safely through the gate and close it behind them, that leaves their only real source of information on how this happened coming from whatever prisoners they've managed to take, most of whom are presumably not specialized in genetic engineering or portal construction and can't be relied upon to have more than a layman's understanding of the subject. If that and whatever corpses and material they capture isn't enough to duplicate the work, in the best case that risks them leaving an unimaginably* enormous amount of value on the table, forever, and in the worst case gets Civilization is destroyed by another attempt having given up their only opportunity to prevent it.

On the other hand, weighing against those uncertain losses and gains are the very real and immediate issues of a lot of people dying, including true deaths. They're not going to underweight the possibilities here, dath ilan works very hard to be about to properly compare counterfactuals and only do time discounting when it's actually warranted, but it remains the case that - presuming that the withdrawal doesn't come to a halt if they reduce the pressure too much - the operation is no longer in service of the objective it was planned to fulfill, and at the very least that ought to adjust the risk-reward calculations here. There's a strong push to scrap the whole affair.

*Used here both in the sense that it's an enormous sum with too many moving parts along too many axes of unknown information to readily visualize, and also in the sense that saying this phrase aloud in dath ilan has the cached response "skill issue."

Are you really going to deontology this, now of all times? Sometimes you have to shut up and multiply, and even with all the uncertainty we both know what the markets are saying here about our expected outcomes if we leave them unimpeded.

Are you really going to give up that easily? I thought this was supposed to be an assembly of the greatest minds in civilization, but the best plan we can come up with for this has dozens of deaths priced in outside of the tail risks? 

I'm not saying it's easy. I'm saying it's our job to shut up and do the impossible.