The grain of truth is that Romans and wagon builders and etc all determined that somewhere vaguely between 4 and 5 feet was an optimal width for vehicle axles.

The grain of truth is that Romans and wagon builders and etc all determined that somewhere vaguely between 4 and 5 feet was an optimal width for vehicle axles. Which is not really a "standard", especially given Romans didn't even have a universally standard measurement system, but to a degree it's an interesting case of convergent design. Obviously people just love simple explanations and latching onto goofy conspiracies though are going to love drawing a straight line between any two points.