Shortly after the opening of the first railway in Switzerland, each region began to favour a separate north-south link through the Alps towards Italy.
Eastern Switzerland supported a line through the Splügen Pass or the Lukmanier Pass, Central Switzerland and Zürich favoured the Gotthard Pass and Western Switzerland supported the Simplon route.

In 1871 the first line was completed through the Alps, connecting Italy and France with the Fréjus Rail Tunnel.

The Compagnie de la Ligne d'Italie was founded in 1856 to build a connection between Romandy and Italy through the Canton of Valais and the Simplon.
On 1 June 1874, it was taken over by the Simplon Company (French: Compagnie du Simplon, S), which  was created to promote the project.
This merged in 1881 with the company Western Swiss Railways (French: Chemins de Fer de la Suisse Occidentale, SO) to create the Western Switzerland–Simplon Company (French: Compagnie de la Suisse Occidentale et du Simplon, SOS).
The French financiers of the SOS were able to secure finance for the tunnel in 1886.
The company considered 31 proposals and selected one that involved the construction of a tunnel from Glis to Gondo, which would have been fully in Switzerland.
From Gondo it would have continued on a ramp through the Divedro valley down to Domodossola.

At a Swiss-Italian conference held in July 1889, it was agreed, however, to build a nearly 20-kilometre long (12 mi) base tunnel through the territory of both states.
In order to secure credit for the tunnel, the SOS joined with the Jura–Bern–Luzern Railway to create the Jura–Simplon Railway (French: Compagnie du Jura–Simplon, SOS).

The participation of the Swiss government led to the signing of a treaty with Italy on 25 November 1895 concerning the construction and operation of a railway through the Simplon from Brig to Domodossola by the Jura–Simplon Railway.
The route of the tunnel was determined by military considerations so that the state border between the two countries was in the middle of the tunnel, allowing either country to block the tunnel in the event of war.

On 1 May 1903, the Jura-Simplon Railway was nationalized and integrated into the network of the Swiss Federal Railways (SBB), which completed construction of the tunnel.
Shortly after the opening of the first railway in Switzerland, each region began to favour a separate north-south link through the Alps towards Italy. Eastern Switzerland supported a line through the Splügen Pass or the Lukmanier Pass, Central Switzerland and Zürich favoured the Gotthard Pass and Western Switzerland supported the Simplon route.
In 1871 the first line was completed through the Alps, connecting Italy and France with the Fréjus Rail Tunnel.
The Compagnie de la Ligne d'Italie was founded in 1856 to build a connection between Romandy and Italy through the Canton of Valais and the Simplon. On 1 June 1874, it was taken over by the Simplon Company (French: Compagnie du Simplon, S), which  was created to promote the project. This merged in 1881 with the company Western Swiss Railways (French: Chemins de Fer de la Suisse Occidentale, SO) to create the Western Switzerland–Simplon Company (French: Compagnie de la Suisse Occidentale et du Simplon, SOS). The French financiers of the SOS were able to secure finance for the tunnel in 1886. The company considered 31 proposals and selected one that involved the construction of a tunnel from Glis to Gondo, which would have been fully in Switzerland. From Gondo it would have continued on a ramp through the Divedro valley down to Domodossola.
At a Swiss-Italian conference held in July 1889, it was agreed, however, to build a nearly 20-kilometre long (12 mi) base tunnel through the territory of both states. In order to secure credit for the tunnel, the SOS joined with the Jura–Bern–Luzern Railway to create the Jura–Simplon Railway (French: Compagnie du Jura–Simplon, SOS).
The participation of the Swiss government led to the signing of a treaty with Italy on 25 November 1895 concerning the construction and operation of a railway through the Simplon from Brig to Domodossola by the Jura–Simplon Railway. The route of the tunnel was determined by military considerations so that the state border between the two countries was in the middle of the tunnel, allowing either country to block the tunnel in the event of war.
On 1 May 1903, the Jura-Simplon Railway was nationalized and integrated into the network of the Swiss Federal Railways (SBB), which completed construction of the tunnel.
Simplon Tunnel