Siegfried line is a boundary line around:

The Siegfried Line, known in German as the Westwall, was a German defensive line built during the 1930s opposite the French Maginot Line. The name derived either from a German defensive position of World War I, the Siegfriedstellung. The Siegfried Line stretched more than 630 km (390 mi) and featured more than 18,000 bunkers, tunnels, and tank traps.