Cool! ...nice to see you recount the story of the ghostly Roman soldiers marching through a cellar in York, England, in 1953. I remember reading about that a few years back, and it was reckoned to be the "oldest" haunting known - at least in England.
People say that some ghosts might be echoes recorded by buildings, especially stone ones. So, here's my angle on why the Roman apparations are still hanging around (or marching around lol) -
Above-ground environments are subject to external factors such as the elements and man-made "vibrationary" pollution etc., but deep down in that cellar it's peaceful and undisturbed over the centuries .... hence the Romans can carry on on their repetitive march, without any of the usual above-ground "interruptions" to gradually dilute their vibrations as time plods by.
And, maybe there are other cellars, too, in other locations where there are also far earlier buried remnants of settlements or forts etc., with their own "garrisons" et al.