Bietschtal viaduct BLS, Iron railway bridge in Raron, Switzerland

The Bietschtal viaduct is a two-track steel railway bridge on the southern ramp of the Lötschberg mountain line in the canton of Valais. It spans the gorge of the Bietschbach at a maximum height of 78 m above the valley floor, with a 95 m central arch and two 35 m approach spans. A narrow footpath runs along its valley side, and tunnels stand at both ends.

Built between 1910 and 1913 by Albert Buss & Cie. of Basel for the Bern-Lötschberg-Simplon-Bahn, the bridge opened as a single-track structure, though its 95 m central arch was already sized for double track. Between 1979 and 1985 the two 35 m approach spans were rebuilt, the valley-side track was lowered by 44 cm, and rivets were replaced with high-strength bolts, raising the weight from 1000 to 1400 t. The second track opened on 8 October 1985 and the original track, reinforced, reopened on 19 September 1986.

The Swiss government recognizes this railway bridge as a class B cultural property, noting its regional significance in the architectural heritage of Raron.

The bridge carries trains over the valley and can be seen from the Lötschberg railway line or nearby hiking paths. Visitors can observe the structure while traveling by rail or walking near Raron.

The bridge's central arch was built wide enough for two tracks from the start, though the line opened single-track in 1913. The Faller model railway company reproduces the viaduct in H0 scale, 1100 mm long and 255 mm high, and later added an N-scale version.