Fortifikation Hauenstein, Military fortification system in Basel-Landschaft and Solothurn, Switzerland

Fortifikation Hauenstein is a 48-kilometre defensive line on the Jura heights around the Unterer and Oberer Hauenstein passes, built from 1914. Its 66 trenches formed a semicircular bridgehead north of Olten, with open and covered positions for 126 guns and eight telephone exchanges. The field works were finished by November 1914; by August 1917, 39 casemates had been completed.

The fortification system was built starting in 1914 as Switzerland sought to protect its neutrality during World War I through military preparedness. The complex remained a key element of Swiss defense strategy for many decades afterward.

The site reflects how Switzerland prepared itself militarily during World War I and shaped the landscape with defensive structures. Visitors can observe how these installations were integrated into the terrain as practical responses to perceived threats.

The site is accessible via several marked hiking trails beginning from different locations in the surrounding area. Visitors should wear sturdy footwear as the routes follow hilly terrain and pass through wooded sections.

The Belchenflue lookout was reshaped by blasting into its present form as an observation post. Along the new Belchen south road, militia units left their cantonal coats of arms, still visible today. Building the works took two million labour hours, with 14,000 men and 1,100 horses deployed.