There are a number of viral social media posts (like this one that ask why the US standard railroad gauge width is such an unusual size, and trace it back thousands of years to conclude it is related to the size of Roman chariots and the ruts they made, which influenced generations of successive roads, tracks and railroads through to today.
That explanation, however, seems far too simple to me as I know that a number of countries have different standard railroad gauge widths, though these usually are within a couple of inches, so maybe they do all trace back to the same source?
My answer won't speak to the reason the US railroad gauge is what it is, but I can address the supposed Roman origin story. This exact anecdote is referred to by Eric Poehler, a leading authority in the issue of Roman roads and their uses, in the introduction to his 2017 The Traffic Systems of Pompeii. Reading his take on it will be a better way to address it than I can do here in summary form, but essentially he points to the utter lack of logic in the story, which relies on a time jump from some period in Roman history to the 19th century, and no evidence at any point in between that any system of measurement used in antiquity had continued into the modern era.
In the story you linked to, there is the quote: "Imperial Rome built the first long distance roads in Europe (including England) for their legions. These roads have been used ever since."
So, first: nope. Yes, the Romans built roads in their territories and provinces, yes they were used in part to facilitate military access, and yes, the routes of those roads have proven in many instances to be routes still in use today - but not on the Roman surfaces. Often modern roads go in the same general area as the ancient ones, but not exactly the same route, or there may be places where the Roman road is beneath the modern one (here is an image of ancient portion of the Via Aemilia in Bologna, excavated beneath the modern road surface), but we are not using the Roman road surfaces still today. That assumption is vital to this anecdote's logic, though, since only by using the Roman road surfaces would the 19th century still be subject to the wheel ruts worn into the ancient paving stones. Roman roads were durable and well-built, for sure, but their being used for that long defies any logic and has no supporting evidence.
Second, Poehler disagrees with the logic of ancient vehicle sizes being standardized "or run risk of destroying their wagon wheels." An example he provides notes that the ruts in one road measure 10-15cm wide, which would accommodate many different types of gauge, and he notes the various types of wagons that were preserved in Pompeii and Stabiae by the AD 79 eruption of Vesuvius which show the differing sizes of the vehicles used at the time - which directly refutes the argument in the Facebook story.
So, again; Poehler will say it better than I ever could, and I highly recommend reading his work on this for more information, but to sum up I'll quote him again on why this anecdote persists:
"...stories such as this one also stay popular because of their trivial nature; no one ever has reason to check."
Viva r/AskHistiorians!
Poehler, Eric. 2017. The Traffic Systems of Pompeii. Oxford University Press.
