Silesia often played the part of a no man´s land in military campaigns against the Habsburg empire, and especially in the 17th and 18th centuries it witnessed numerous military campaigns that threatened the very existence of the monarchie. Military conflicts in the second half of the 18th century resulted in the loss of the major part of Silesia. In order to stop further expansion of Prussia into Moravia and Hungary, field fortifications were constructed on the borders, in access corridors of mountain areas. This article presents. on the basis of field, cartographic and archives research, two systems of modern-age fortifications, Hradec and Jablunkov fortifications. Their example demonstrates how the monarchy borders were protected against invasions from Prussia, and how the changes in military strategy and tactics were reflected in the typology and location of field fortifications, frequently employed in mountains regions.