Somewhere on the Belarus border, a Russian train stops and gets its wheels taken off. Hydraulic jacks lift the carriages, workers roll one set of bogies away and slide another set underneath, and about two hours later the train continues into Poland. All of that exists because of eighty-five millimetres. That's the gap between Russian track and almost everyone else's in Europe, and the usual explanation is that the Tsar built his railways wider to keep invading armies out. But the engineers who chose that width left records behind. So why does the invasion appear nowhere in them?