Though the Alps form a barrier they have never formed an impassable barrier, since, from the earliest days onwards, they have been traversed first, perhaps, for purposes of war or commerce, and later by pilgrims, students and tourists. The spots at which they were crossed are called passes (this word is sometimes though rarely applied to gorges only), and are the points at which the great chain sinks to form depressions, up to which deep-cut valleys lead from the plains. Hence the oldest name for such passes is Mont (still retained in cases of the Mont Cenis and the Monte Moro), for it was many ages before this term was especially applied to the peaks of the Alps, which with a few very rare exceptions (e.g. the Monte Viso was known to the Romans as Vesulus) were long simply disregarded.
The native inhabitants of the Alps were naturally the first to use the alpine passes. But to the outer world these passes first became known when the Romans traversed them in order to conquer the world beyond. In the one case we have no direct knowledge (though the Romans probably selected the passes pointed out to them by the natives as the easiest), while in the other we hear almost exclusively of the passes across the main chain or the principal passes of the Alps. For obvious reasons the Romans, having once found an easy direct pass across the main chain, did not trouble to seek for harder and more devious routes. Hence the passes that can be shown to have been certainly known to them are comparatively few in number: they are, in topographical order from west to east, the Col de l'Argentiere, the Mont Genevre, the two St Bernard passes, the Splugen pass, the Septimer pass, the Brenner pass, the Radstadter Tauern pass, the Solkscharte pass, the Plocken pass and the Pontebba pass (or Saifnitz pass).
Of these the Mont Genevre and the Brenner were the most frequented, while it will be noticed that in the Central Alps only two passes (the Splugen and the Septimer) were certainly known to the Romans. In fact the central portion of the Alps was by far the least Romanised and least known till the early middle ages. Thus the Simplon is first certainly mentioned in 1235, the St Gotthard (without name) in 1236, the Lukmanier in 965, the San Bernardino in 941; of course they may have been known before, but authentic history is silent as regards them till the dates specified. Even the Mont Cenis (from the 15th to the 19th century the favourite pass for travellers going from France to Italy) is first heard of in 756 only.
In the 13th century many hitherto unknown passes came into prominence, even some of the easy glacier passes. It should always be borne in mind that in the Western and Central Alps there is but one ridge to cross, to which access is gained by a deep-cut valley, though often it would be shorter to cross a second pass in order to gain the plains, e.g. the Mont Genevre, that is most directly reached by the Col du Lautaret; and the Simplon, which is best gained by one of the lower passes over the western portion of the Bernese Oberland chain. On the other hand, in the Eastern Alps, it is generally necessary to cross three distinct ridges between the northern and southern plains, the Central ridge being the highest and most difficult. Thus the passes which crossed a single ridge, and did not involve too great a detour through a long valley of approach, became the most important and the most popular, e.g. the Mont Cenis, ihe Great St Bernard, the St Gotthard, the Septimer and the Brenner.
As time went on the travellers (with whatever object) who used the great alpine passes could not put up any longer with the bad old mule paths. A few passes (e.g. the Semmering, the Brenner, the Tenda and the Arlberg) can boast of carriage roads constructed before 1800, while those over the Umbrail and the Great St Bernard were not completed till the early years of the 20th century. Most of the carriage roads across the great alpine passes were thus constructed in the 19th century (particularly its first half), largely owing to the impetus given by Napoleon. As late as 1905, the highest pass over the main chain that had a carriage road was the Great St Bernard (8111 feet), but three still higher passes over side ridges have roads -- the Stelvio (9055 feet), the Col du Galibier (8721 feet), in the Dauphine Alps, and the Umbrail Pass (8242 feet).
Still more recently the main alpine chain has been subjected to the further indignity of having railway lines carried over it or through it -- the Brenner and the Pontebba lines being cases of the former, and the Col de Tenda, the Mont Cenis (though the tunnel is really 17 miles to the west), the Simplon and the St Gotthard, not to speak of the side passes of the Arlberg, Albula and Pyhrn of the latter. There are also schemes (more or less advanced) for piercing the Splugen and the Hohe Tauern, both on the main ridge, and the Lotschen Pass, on one of the external ranges. The numerous mountain railways, chiefly in Switzerland, up various peaks (e.g. the Rigi and Pilatus) and over various side passes (e.g. the Brunig and the Little Scheidegg) do not concern us here.
See also: Peaks and passes of the Alps