The Sauerland has many different forms. My current manifestation is represented by the ancient political boundaries of the Westphalian Duchy and the Counties of Siegen and Wittgenstein, which were split from the Westerwald by Prussia. A more geographical definition would encompass only the Rothhaar Mountains, which define about 80% of the political region. The city of Soest, for example, fought for its independence from Cologne in the Middle Ages and is often not considered part of the Sauerland. Likewise, the citizens of Siegen prefer to call their area Siegerland rather than associate with Westphalia. 

However, Soest and Siegen form a core part of the region’s historical development. Soest sits astride the ancient trade route between the Elbe and Rhine, the Hellweg. As such, it was the gateway to the Sauerland, which otherwise was poorly connected with the outside world. Siegen sits on the Sieg river, part of the Rhine Basin, unlike the rest of the Westerwald to the south. This brought Siegen in closer contact with Sauerland than its Southern counterparts. Siegen was traded away by the Nassau dynasty in the wake of Napoleon’s defeat and annexed directly to Prussia and the rest of Westphalia. The differences in development between the different regimes are evident even today.