In the 13th century many hitherto unknown passes came into prominence, even some of the easy glacier passes. In the Western and Central Alps there is only 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 reach the plains, e.g. the Montgenèvre, that is most directly reached by the Col du Lautaret; and the Simplon, which is best reached 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 to cross. 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, the Great St Bernard, the St Gotthard, the Septimer and the Brenner.