The "Via Aemilia" (modern SS 9) still follows its original Roman course as it runs between the hills and the plain; it would have been the obvious course to follow as it was the only major Roman road east of the Apennine Mountains leading to and from the Po Valley. Attempts to deduce the original course of the Rubicon can be made only by studying written documents and other archaeological evidence such as Roman milestones, which indicate the distance between the ancient river and the nearest Roman towns.