Unlike today, there were no fixed borders in the Middle Ages. The dominions (territories) were fragmented and often changed. The basis of it all was the feudal system: feudal lords from the nobility and clergy lent land to vassals. They administered and protected the area, providing their feudal lord with loyalty and military support in return.

At the beginning, the territories were seldom cohesive areas. Instead, they consisted of scattered possessions such as villages, castles or monasteries: that was the case in the county of Saarbrücken too. And that is why there are no coherent borders to be found on the maps from the time when the county came into existence.

Furthermore, there were possessions located in places now called Belgium, Westphalia or Baden, and on the Lower Rhine. Large areas of what is Saarland today were under the control of other lords with varying degrees of influence. What the maps show is greatly simplified and limited to selected periods. For a clearer impression, the focus of the map has been placed on the areas with the greatest and most significant change.