The old stone Roman roads became rutted over long time spans =wheel spacings were dictated by these ruts. Wrong space = broken wheels. Railroads had many early

The old stone Roman roads became rutted over long time spans =wheel spacings were dictated by these ruts. Wrong space = broken wheels. Railroads had many early spacings, from narrow mine rail carts to longer distances. Railways need long gradual slopes 1-3% in most cases. This required causeways as well as cuts. Back in the day rock blasting cuts was very costly = iron drills and black powder blasting = $$$. After dynamite and carbide drill inserts, this became 80% less expensive. Dynamite shattered rock and insert drills cut holes. The old black powder/iron drill made wide cuts = $$$ = need for narrow gage to save $$. Long rail lines in USA led to the need for a common standard. The narrow cuts were blasted wider with dynamite etc, and many were abandoned. There is little connection between Roman roads and various wide/narrow US gages. There are also dual gage rail cars with 3 wheels on an axle - for Russia - Europe cars.