The Pacific Railroad Act of 1863 established that the gauge of the first transcontinental railroad was to be 4'8½", which is I believe the first time the US actually legally established a particular gauge. Some states had established their own (non-4'8½") gauges before then, but it looks like by the eve of the Civil War, 4'8"-4'9" gauge (the various gauges in this range can be treated as identical for rolling stock purposes) was the plurality of track.

By the Civil War, it looks like you have a Midwestern standard gauge, a Northeast standard gauge separated into two islands by a I think 5'6" New York/New Jersey gauge, and Ohio using a 4'10" gauge separating these two networks; the South's network--which is far less dense--is 5' gauge; and now you get transcontinental railroads being planned for a 4'8½" gauge. Now it is true that the Southern railroads largely switched to the 5' gauge as a result of connecting to the original few lines that connected isolated lines being 5', but a similar process in the North also broke up the non-standard gauge areas, and between the much smaller track area of the South and the fact that there were almost no 5' lines outside of the CSA, it is incredibly unlikely that the creeping 5' would ever have been adopted in the US.

(From attempting to browse the Confederacy's laws, I don't think they ever fixed a gauge for the routes they authorized to be completed).

I remember in the summer of 89 having to wait several hours in Uzhhorod for exactly this reason. I don't remember if they kicked us of the train or if we wanted to use the opportunity to do some sightseeing, but there were no sights to see in Uzhhorod in 1989. The most notable thing we found was a local "wall of shame": a display case with pictures of local miscreants, together with the listings of their crimes. Being at the height of Gorbachev's prohibition, the most common crime was "drinking alcoholic beverages in public". I think that if I had to live in Uzhhorod in late 1980's, I would probably end up drinking alcoholic beverages in public as well.

Yes, there are many 'break of gauge' points. They're mainly for historical inertia and economic reasons, but the military impediment is a known side effect. https://en.wikipedia.org/wiki/5_ft_and_1520_mm_gauge_railway...

Seems slow. I went by (night)train from Bonn/Cologne via Belgium to Paris, France, and from there to Madrid, Spain. Which involved that bogie change thing in Hendaye/Irun at the French/Spanish border. Took maybe 45 minutes. In 1980/81.

If you walk around Pompeii, the paved streets still have ruts from wagons being driven through them, and the ruts seem to be fairly close to the standard railway gauge. Certainly close enough to provoke the idea.

I’m fairly certain it’s because a wagon wider than you are tall just feels unnatural.

' in 1845, Robert Stephenson made the following statement: “If I had been called upon to do so, it would be difficult to give a good reason for the adoption of an odd measure — 4 feet 8 and a half inches.” '

Well, the half inch is accounted for , but not the original 5' plateway.

I think that the meme even had legs in the first place is due to the fact that 4'8½" is an objectively weird gauge--why the ½"? That the 4'8½" track gauge can be traced to Stephenson's decision isn't hard to figure out, nor is the fact that there is some measure of continuity between older forms of railway-like systems and railways. I expect that the meme came about from someone interpolating those facts to assume that the 4'8½" gauge came from a precise reconstruction of some Roman thing, since it's also decently common knowledge that Roman units are not the same as imperial units. The rest of the meme (tying this fallacious history of the track gauge to the size of a rocket part) is very obviously complete balderdash to anyone with a modicum of railroad engineering.

Or put more succinctly:

The original meme: 4'8½" exists because exact replica of Romans.

The truth: As laid it, it was originally exactly 5'. But we changed what we use to measure gauge, so it's now reported as 4'8". Stephenson changed that to 4'8½" because that allowed him to fix a problem he had without having to replace anything.

And honestly, "cheap engineering fix" is a more interesting explanation to a conundrum than "Romans."

I’m a little disappointed none of the train museums I’ve visited have mentioned plate ways or wagon ways.

https://en.m.wikipedia.org/wiki/Wagonway