of the Benrath line, separating High German from Low German, where high refers to the geographically higher regions of the German-speaking area of those days (combining Upper German and Central German varieties - also referring to their geographical locations). North of the Benrath line up to the North Sea, this consonant shift did not happen. The Walser migration, which took place between the 12th and 13th centuries, spread upper Wallis varieties towards the east and south, into Grisons and even further to western Austria and northern Italy. Informally, a distinction is made between the German-speaking people living in the canton of Valais, the Walliser, and the migrated ones, the Walsers (to be found mainly in Graubünden, Vorarlberg in Western Austria, Ticino in South Switzerland, south of the Monte Rosa mountain chain in Italy (e.g. in Issime in the Aosta valley), Tirol in North Italy, and Allgäu in Bavaria). Generally, the Walser communities were situated on higher alpine regions, so were able to stay independent of the reigning forces of those days, who did not or were not able to follow and monitor them all the time necessary at these hostile and hard to survive areas. So, the Walser were pioneers of the liberalization from serfdom and feudalism. And, Walser villages are easily distinguishable from Grisonian ones, since Walser houses are made of wood instead of stone. Phonology Consonants Like all other Southern German dialects, Swiss German dialects have no voiced obstruents. However, they have an opposition of consonant pairs such as and or and . Traditionally, that distinction is said to be a distinction of fortis and lenis, but it has been claimed to be a distinction of quantity. Swiss German keeps the fortis–lenis opposition at the end of words. There can be minimal pairs such as 'straight' and 'arête' or bis 'be (imp.)' and 'bite'. That distinguishes Swiss German and Swiss Standard German from German Standard German, which neutralizes the fortis–lenis opposition at the ends of words. The phenomenon is usually called final-obstruent devoicing even though, in the case of German, phonetic voice may not be involved. Swiss German are not aspirated. Aspirated have (in most dialects) secondarily developed by combinations of prefixes with word-initial or by borrowings from other languages (mainly Standard German): 'keep' (standard German ); 'tea' (standard German ); 'salary' (standard German ). In the dialects of Basel and Chur, aspirated is also present in native