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.)