At 8:16 AM local time, there's a distortion in the air. A keen observer might analogize it to a heat haze, though in truth the resemblance is more superficial than anything else. 

 It lingers for about thirteen minutes, passively observing its surroundings, and then sets off. In motion, the stealth is significantly less effective, but it still serves the role of disguising just what is doing the moving, and whatever is causing the visual distortion appears bright enough to be careful of the sightlines of passerby and make good use of cover, shadows, and blind corners as it makes its way down unfamiliar streets. Does anything interfere with this?

A few dath ilani spot some movement out of the corner of their eyes, but nothing in particular comes of it. The city's cameras get a much better view of things, of course, but there isn't anyone watching their feeds live with enough care to flag it as unusual.

The shimmer sticks around for over an hour, though a lot of that time is also spent on stationary observations from better viewpoints. It ranges a few blocks from where it first made its appearance, circles around, and then makes a return to the location it first manifested to disappear completely. By 9:37 AM, there's no sign it was ever there.

Absent any information to nudge it off its tracks, the inhabitants of Schelling Point continue to go about their day in the manner they are accustomed to. Those who welcome the warmer weather make their way outside, for lunch if their schedule doesn't otherwise permit it, while others make use of the city's large underground transportation network to avoid its rays. Surge pricing pushes the average cost of chilled drinks and treats up 2%, but the predictability of the change in consumer habits means that most of the increased demand is absorbed by increases in throughput.

At 11:23 AM local time, a large marble structure supported by columns appears in the middle of a busy downtown street. The people taking up the space find themselves suddenly elsewhere, and a battalion of armored men on horseback stream out of the structure and into the city proper. No trumpets herald their arrival; the scout didn't mention any nearby military positions, but the best way to minimize their losses is to make the most of the time until that changes, so their fastest elements are set towards making contact with their opposite numbers and running down any isolated detachments.

The local residents will get out of their way, or they will be run over.

What the superheated toilet paper?

Earlier and elsewhere:

To be a noble of the Saderan Empire is to be an heir to the greatest military legacy the world has ever seen. For seven hundred years, the Saderan dragon has issued forth from the imperial city to spread the Empire's glory, and for seven hundred years, never has there been a defeat they could not expunge. Even now five thousand miles separate its eastern border from its westernmost extent, and those nations beyond its borders deliver regular tribute to ensure that status endures. Every aristocrat's childhood is filled with the tales of those heroes that achieved such victories, and of all the imperial offices, there are few more coveted than the right to command a legion. 

It doesn't usually feel that lucky to Legate Cattaneo, but from the sound of things, today might be the day that that changes.

The biggest thing they never tell anyone about being a legate is how hard it is to actually be a conquering hero in this day and age. The other downsides are nearly impossible to miss, from the immense bribes required to get the title to what feels like every other noble in the empire jumping on even the tiniest display of weakness, but somehow he'd always managed to delude himself on this score prior to getting the job. You wouldn't think it from looking at a map, after all; even the least adept cartographers were happy to display a dozen other countries on their maps, and none of them held a candle to the might of the legions, so by all rights they ought to be ripe for the picking. It took a closer and less rose-tinted examination to see the flaws that constantly bedeviled him, and no doubt had done the same to a number of his predecessors. 

Right off the bat, you could cross a full third of them off the list with prejudice. Those countries might have had their own kings or queens, but they were the Emperor's vassals in every way that mattered. Their men wandered the court and senate with impunity, ensuring they would know your plan before you even got to mustering, and the emperor was more than happy to take their lavish gifts in exchange for discouraging any foolish adventurism from his generals. It wasn't even really possible to count on victory to wipe away the stain of disobedience, because their taxes were already flowing into the imperial coffers and even hiking up the rates wouldn't make up for the shortfalls a war would cause. It could still be done, of course, but one might as well set their eyes on a neighboring governor for their trouble, especially since given a hundred years to copy the Empire even lesser nations could figure out the basics of a proper army. That left only the far-flung barbarian kingdoms as real options, and none of them came without strings attached. Marching a Legion three thousand miles across the continent to fight a war was expensive, to say nothing of the difficulties in procuring food, and with how little loot they had to go around you'd have to be able to cover most of the finances out of pocket, all for the glory of conquering some territory nobody in Sadera had ever heard of. There were always exceptions to any rule, but his fellow legates were not in the habit of leaving good invasion targets unmolested for long, and absent a miracle the best you could hope for was to imitate Prince Zorzal and just eat the cost of a ruinously expensive conquest to come out with a win. 

Legate Cattaneo hadn't been expecting to get his hands on a miracle like that, but given the proper motivation his augurs and magi had come through for him in a big way. A divine gateway to another world, one where nobody had heard the first thing about how to deal with imperial dragon knights or a proper tortoise formation? It didn't matter if he could hold it or not, even a sufficiently successful raid on another world could garner him the kind of status none of his peers had managed in almost a century, or else the wealth to parlay into another conquest entirely. He could practically see a marriage into the imperial family on the way, to say nothing of the wealth and senatorial standing, and he'd be damned before he let it slip through his fingers.

Fortunately for his ambitions, the gods had truly smiled upon him. The first stroke of good fortune was the location - Alnus hill was only two hundred miles south of Italica, so getting everything he needed into position would be simplicity itself, but it was also far enough away from the imperial capital that he wouldn't raise questions about if he was planning a coup. The second was the sheer size of the aperture in question at its greatest extent; the image brought to mind by 'gateway to another world' was far smaller than what it proved able to manage, to the point that he wouldn't have any issues with getting the wyverns through and the cavalry could ride ten men abreast. It would let him make the most of the element of surprise, especially the first few critical minutes, and would hopefully be enough to prevent any elite detachments from slowing them down by holding a chokepoint. The third stroke of good fortune was that the local rector was a yellow like he was. It was hardly the tightest factional bond, and he had certainly never met the man other than in passing prior, but some of his friends knew their friends and some favor trading was enough to get local support in his preparations.

And so it was that, on the morning of the 14th day of the 6th month of the 687th imperial year, 17th Duncanica Legion arrayed itself for battle and waited for the return of its scouts. A potent force even in times of relative peace, its numbers had swollen with mercenaries, local auxiliaries, and temporary transfers until it numbered almost half again its usual size. Though as always the it was the heavily armored human infantry that made up the core of the army's strength, they were joined by orcish archers, heavy and light cavalry, three different detachments of wizards, ogre siege companies, and as many dragon knights as the legate could tempt away from their ordinary duties.

All together they made nearly twenty-five thousand heads, which some might call it excessive, but he disagreed. For all that the history of Falmart was littered with countries that had been conquered by less, it was also littered with the corpses of generals that had taken the favor of the gods for granted and not ensured that their victory was sufficiently certain. Their blessings could be fickle at the best of times, so while he made sure sacrifice generously in the days prior he had also made sure to supplement that with careful preparation, from endless drills to the coveted illusionist wizards making their report to him right now. There was always something up to chance, but if Legate Cattaneo had his way this battle would be entirely one sided.

Again, what the superheated toilet paper?

There's a cavalry battalion charging out of a weird archway that suddenly appeared in downtown Schelling Point. And if you don't get out of the way, you're going to get run over.

...So, a team of aggressive horse-racers wearing primitive protective gear and some kind of... sports equipment just appeared out of thin air and charged into a busy street? That feels incorrect but we have so many overlapping confusions here it's not trivial to disentangle them, even to the point of figuring out how to test the moving parts of that hypothesis. They're very big and moving very recklessly, though, so we're definitely getting out of the way; our insurance injury premiums would go up a little even if theirs pays out for them being obviously at fault, and also it seems like it would hurt. It should be fine, obviously they don't want to hit anyone either.

Of course not. They're an elite military detachment, here to take down as many defenders as possible before the city has time to rally a proper defense; they don't have time to waste on random passerby. They're just not going to go out of their way to avoid it either, especially not if it means slowing down.

The streets aren't so crowded there isn't any room to move out of the way, and further off people making room for the people displaced by other people moving out of the way is just another coordination problem, but a few people still aren't light enough on their feet and get hit by a glancing blow from most of a ton of metal and muscle moving by at speed. Some of those screams definitely imply broken bones.

When you're experiencing events wildly out of agreement with consensus reality, the general suggestion is to loudly announce tsi-imbi and avoid any actions that, if you are hallucinating, might result in you hurting real people. Portals don't actually open up in the middle of busy streets, but people do sometimes experience psychotic breaks that render them unable to distinguish what's really going on. Along the street, usage starts picking up; it's not most people by any means yet, but even the ones who wouldn't go that far are very confused.

(People are still going to go help the people who got injured, though, obviously, and call emergency services.)

They don't speak the language, and any attention they have to spare from their task is going towards just how godsdamned weird this city is; humans acting slightly weird doesn't rate in comparison. If it's important, the infantry will have to deal with it.

Said infantry are, naturally, the next group through the gateway. Given the emphasis on haste, one would be forgiven for expecting the dragon knights to be next, but such assumptions rest on a fundamental misunderstanding of imperial tactics and ignorance the material reality that underlies them - that wyverns are expensive.

From the small clutch sizes that make it difficult to expand their population to the immense number of calories required to sustain their active metabolism and flight, behind every dragon knight in the legions is a lies a fortune invested over decades prior by some imperial noble house allied with the legate. Compared to such princely sums even maintaining a warhorse begins to seem positively affordable, which is Saderan doctrine has always been to take the utmost care with their use; cautious, measured deployments to favorably balance risk and reward, followed by overwhelming force to break the enemy morale and chase down the scattering survivors. If instead the wyverns went first and were ambushed when going through the gate - grounded, in small numbers, in a city held by the enemy - he could in one stroke cripple his most capable forces and anger his most important allies.

And so on the heels of the cavalry legionaires begin to stream into Schelling Point at a steady jog. What resistance do they encounter?

It would be an exaggeration to describe any part of today as predictable, but whatever the cause of the sudden street building, it's pretty clear that staying nearby is going to be at least moderately hazardous to your health. Most of the populace has backed off, leaving only a small curious contingent to examine the structure. Even at a closer glance, it still looks like stone, and it's not entirely clear how it was hidden and/or faked. If it's a prank, it's a fairly high effort one of the sort people more often tend to imagine doing than usually pull off.

(A prank is the leading umbrella hypothesis here, with shares on 'yes' already trading at about 70%; while the hows and whats are still up in the air, it's a rare ilani who doesn't understand the appeal of pulling off something seemingly impossible to make someone else's day that much more surreal).

I guess that technically counts as resistance.

The civilians can get some nonlethal spear prodding to move them away from the gate; they seem mostly fit enough it'd be a waste to kill them, but the centurion will have their hides if they're dumb enough to start looting and taking captives before the position is secure. Orders say they need a good bit more space before they start setting up the barricades or there won't be enough room for the wyverns to take off, so the gawkers are going to have to move a block or two.

Superheated - Ow! The jabs don't seem to be aiming for vitals, but nonlethal doesn't mean not painful, and even the ones that aren't drawing blood are going to bruise.

"What's the big idea here?" 

Even for a prank of this magnitude, that's going way too far; he's going to sue their pants off for this nonsense.

The barbarians are presumably saying something, but it's just so much noise to imperial ears; even the ones that know some of the regional creoles aren't parsing anything meaningful, and wouldn't be inclined to care if they did.

Ow, ow, ow. A number of people nearby do have some level of combat certifications, but when dath ilani drill those skills it's typically self-defense-only or group-safe-subdual courses and neither are predicated around fighting an organized group with weapons while unarmed; the usual advice there is "don't." There are more calls going through to emergency services now, because even without new pertinent details each reporter can still move their internal prediction market about whether this is actually happening, and more bystanders are going to join in on recording. That doesn't seem to be provoking a reaction from whatever this group is, at least, and if you predictably refrain from recording events because other people seem to have it covered then it'll turn out tomorrow that the only people with recording were working with whatever group pulled off the stunt and none of the footage shows anything they didn't want it to.

Elsewhere in Schelling Point:

In another circumstance, Mylonas would perhaps be willing to admit there was a certain humor in the situation. There were no shortage of ways a city's defenders could make the lives of cavalry hell, and some part of him had been dreading an encounter with foreign magics or battlements of archers or tight ranks of heavy infantry ever since he first learned of his role in the Legate's plan, but never had he expected that the largest roadblock in his efforts would be the vagaries of foreign architecture of all things. If you'd mentioned it to him yesterday, it would never have come to mind as an issue! After the third false start, however, he was forced to face facts - he had absolutely no idea where to even find the local administration. To his untrained eye every building in the city was practically the same, and his efforts to search those that stood out from the pack had thus far turned up a library, an indoor market, and what was presumably some sort of barbarian ritual space he didn't remotely have the context to recognize.

The locals weren't any help  - he and his men could scare them, no problem, but not one among them would admit to knowing a civilized language no matter the pressure. He'd have thought "take me to your leader" wouldn't be hard to grasp from a group of invading soldiers, but they weren't terribly smart either, and even killing a few of them didn't get the rest to wise up. Perhaps a scholar or soothsayer could get something out of the resulting babbling, particularly given the common threads therein, but 'see imbeye' was so much gobbledygook to his ears and the more comprehensible screaming didn't exactly give him new information. The only real positive of the affair was the lack of resistance - if the city did have a standing garrison, it was either well away from the downtown area or asleep at the reins, and both cases meant they could rest relatively easy when it came to retaliation. There would be time to join in on looting the place, at least once they'd done enough searching that they could defend their failure to capture the local magnates.

Schelling Point emergency services is aware of the problem. It would be an exaggeration to say they understand the situation, but they have a lot more to go on than most of the people on the ground; there are quite literally hundreds of people around the city relaying their observations to the authorities, and they've supplemented this with an emergency protocals that give them access to (almost) all the cameras in the city. Within two minutes of the mysterious building first appearing, the situation was emergency services' top priority; within five, they had already escalated it to exception handling and started roping in keepers. 

The fundemental problem about dealing with it is that it's impossible. Forget the thing it's presenting as being, which is ludicrous on its face; how you'd go about convincingly faking the evidence they're getting is still unclear even having seen it done. They've already done the tests to rule out the worlds where it's an disciplined conspiracy of supercriminals with one good trick; you've got to posit an enormous group of supercriminals of unprecedented organization that also have multiple undiscovered tricks, and even once you posit that being true it doesn't really make them any less confused about what's going on. They're not all keepers, but even the average dath ilani is good enough at cognitive self-reflection to notice the problems there. And while it's typically considered best practices with confusing situations to make small, careful changes to iterate your model until it starts cohering, the 20th percentile guess is that true lives are at stake and the upper plausible limit on the number is alarmingly high.

So you're paralyzed with indecision?

No, of course not. Even children are capable of figuring out that not deciding on a course of action is usually one of the worst possible ones in a crisis, and emergency services is exceedingly well drilled at avoiding that particular pitfall. What they're explaining is why governance is not currently scrambling an airstrike.

By the standards of its technological contemporaries, dath ilan's military is one of the least impressive parts of their civilization. They possess few grand fortresses, can speak of no great glories won in battle, and do not march in grand ranks. Across the entire world, and even including those civilian positions necessary for keeping the machine flowing within their numbers, less than a tenth of a percent of dath ilani are employed by the military at any given time, and even those slated for combat roles have often rather anemic ordinances.

Much of the reason for that is from a lack of need, but that's not the entire story. Certainly dath ilani have all been under one government for longer than recorded history*, so its deployments and procurement need only consider responding to infrequent internal threats, but even those strictly limited and knowable threats could justify a larger force. It's not even a question of money, either; certainly civilization would prefer not to spend resources inefficiently, but the rates at which they will trade their enormous wealth for preserving lives - even stochiastically, for most would not consider it a critical distinction - would stagger belief. Instead the reasoning is rather more structural, in that dath ilan does not in fact want its government to have a monopoly on force. Certainly all else equal they would prefer the armed forces capable of dealing with emergencies, but not at the cost of enabling it to stay in power without the support of the population at large, and the role a hostile military could play there is obvious even to people who phone in their efforts when it comes time to practice overthrowing the government. And since a key part of keeping those counterfactuals strictly counterfactual is ensuring nobody is incentivized to try it, there are an enormous number of checks on the army to limit what it can do, and especially what it can do in a hurry on governmental orders based on fantastical information.

One of the key consequences of this is that it's not exactly trivial to bomb one of their own cities** even if they wanted to. They could manage it once, if everyone involved in the decision making were to have themselves imprisoned pending trial to accomplish it, but - even if everything were exactly as it bafflingly seems, the difference between handling this alien attack optimally or not is conservatively thousands of lives. (There's also some significant concern about whether it would even work out that way - spears and arrows are not a particularly terrifying armament, but an army best modeled by that capability wouldn't appear without warning from a space that absolutely could not fit them with no prior records of their existence).

*A significantly less impressive timespan than it might sound, though the planet has indeed been unified for a while.

**With one notable exception, but it's the thorough hope of everyone involved that that particular contingency will never be needed.

And so for now the missiles remain unfired, even if not all the planes that could launch them are still on the ground, and a similar forbearance goes for most of their other indiscriminate weaponry. This leaves emergency services with the unenviable problem of time. Civilization does technically have plans for dealing with an alien invasion, but the assumption has always been that by and large such an event was unlikely to occur and beyond their ability to win if it did. Between dath ilan and a civilization already capable of crossing the stars... there's only so much you can do at the other end of a power gap that large, even before you consider the fact that any opponent not confident in their ability to win such a fight could trivially avoid picking it. They're putting together new plans almost as fast as the new information flows in, but they're new plans, and the difficulty of logistics in haste is as always a problem. Everything more complicated than evacuating the city is going to take longer than anyone involved would like.

And in the mean time-

Yeah. People are going to die. 

Just be glad this isn't one of the legions that likes to take skulls as trophies.

...They had not been tracking that as one of the ways this could have been worse. Why would anyone do that?

Tribune Benatus is not, exactly, satisfied with the status of the gate fortifications. It's not that they're bad work, by any means, though he's confident he could have done significantly better if they weren't racing against time - having a ready stockpile of construction materials goes a long way. The problem is the blasted city. Whatever bizarre local concrete they use to pave the streets is the next best thing to impossible to dig through without magical tools, and for some Hardy-damned reason they put it everywhere, limiting how much he'd trust the walls against any siege equipment. He doesn't trust the local buildings they've taken over as hardpoints either, not with how difficult the bigger ones are to properly sweep and the risk of an aerial insertion. It'd be better if they could just block off the staircases, but then anyone who could get there would have free reign to start raining down arrows or pitch or whatever improvised ammunition came to mind down on his people's heads, so he just has to live with the uncomfortably large troop detachments they require.

Still, perfect is the enemy of good, and unless his men missed an invisible mage there's nothing in position to threaten the gate right now. He gives the order to let the dragon riders off their leash, and the steady stream of soldiers and materials into his base camp parts to allow the enormous beasts room.

Finally.

Wait, no, back up a second here. Are those wings?

Yes? How else would they fly, hydrogen sacks?

It's not that it's inconceivable, so much as... flying creatures exist under a handful of very tight constraints, and large animals capable of powered flight don't look like that. Dath ilan has fossil evidence of a handful of species in roughly the right ballpark of size, and they all shared key traits by necessity.

Firstly, they need to have large enough wings for their size and a sufficiently aerodynamic body to have enough lift to stay aloft. Something around fifteen to one in lift per drag, in the ideal case, but certainly not less than five. Secondly, they need to be light. Every kilogram of mass in their body is another 10 newtons their muscles need to offset whenever they want to gain height, and flapping your wings is not the most efficient way to supply thrust imaginable. And thirdly, particularly if they do a lot of taking off from ground level, they need enormously powerful wing muscles. These “wyverns” fail all three, even before you consider the fact that they're carrying a rider (!) wearing heavy metal armor (!!) into battle. And you can't just say that it's genetic engineering, either; a modern sailplane can be enormously more efficient than any bird at flight, but the way it does that is by having a very precisely engineered shape, which again does not look like a wyvern.

That's a bit of an exaggeration. They do make heavy concessions to the rider's weight; much like a horse jockey, the ideal imperial dragon rider is short and slender, and their kit is stripped down as close to the bone as possible. Their armor is made of bespoke plate, ruthlessly optimized to only cover what it must and enchanted for strength so it can be hammered thin without compromising the defense. Their saddle is simple and unornamented, sufficient to allow them to stand in their stirrups and prevent the wyvern's scales from chafing against their clothes, and little more. And the weaponry - oh, there the compromises run tight and dear, much to the dismay of every enterprising legate with the idea of dropping rocks or tar or flaming oil on their foes. This also gives insufficient credit to the muscles the wyverns do have, and the powerful metabolism that fuels them - a wyvern can easily eat an unsuspecting noble family out of house and home.

And?

And they're the chosen of the sun god Flare, though he rarely bestows his direct favor on any save for true dragons. If you think these are bad, you're in for a rude awakening later.

...Noted.