The San Boldo Pass and the “Road of 100 Days”

A mountain pass in the Belluno Pre-Alps where the history of the First World War meets one of the most daring feats of engineering of the twentieth century.

Some roads tell stories. And then there is the San Boldo Pass — a road that is itself a story: of war, of ingenuity, of human toil, and of time compressed into one hundred feverish days during which thousands of men transformed the rock of the Treviso Pre-Alps into a masterpiece of military engineering.

Driving it today — by car or motorbike — is an experience that blends the thrill of the road itself — its tight hairpin bends, the tunnels cut straight through the rock, the walls that seem to close in overhead — with the awareness of standing in a place that history has marked deeply.

A project conceived in peacetime, completed in wartime

The story of this road begins even before the cannons started thundering on the Italian front. In 1914, Italian engineer Giuseppe Carpenè had already drawn up plans for a carriageable road connecting the Val Belluna with the Treviso foothills via the San Boldo pass. The goal was essentially commercial: to open a communication route between two territories separated by the Pre-Alps.

Then came the war. And with it, everything changed.

After the Italian rout at Caporetto in October 1917, the front collapsed back to the Piave river. The Belluno area fell under Austro-Hungarian occupation, and the San Boldo pass — with its ready-made project already on the table — became a first-order strategic priority. Linking the rear lines to the front meant being able to move supplies, troops and artillery in the shortest possible time.

One hundred days, seven thousand men

The Austro-Hungarian command entrusted the construction to the engineer corps, led by Lieutenant Colonel Nikolaus Waldmann, commander of the Straßenbaugruppe (Road Construction Group). Work began on 1 February 1918 with unprecedented intensity. Around seven thousand people were mobilised: engineer troops, Russian and Italian prisoners of war, and local inhabitants — including women, elderly people and children — conscripted for forced labour.

They worked in continuous shifts, day and night, with rudimentary tools. The rock was broken by hand and with explosives. Materials were carried on men’s backs up the hillsides. In one hundred days — from 1 February to 1 June 1918 — the road was complete.

Carpenè’s original design was taken up and adapted to new military requirements. The result was a road of roughly 15 km featuring five curved tunnels blasted through the rock — a work that, even with today’s technology, would be considered a bold undertaking. The road had to achieve a steady 10% gradient, steep enough to challenge the imagination, yet gentle enough for artillery to pass.

What visitors find today

The road that visitors drive today is, at its core, essentially that of 1918. The five tunnels cut through the rock — some so narrow that only one vehicle at a time can pass — still have the rough, austere look of a wartime construction. The traffic lights controlling the alternating one-way system are the only concession to modernity along a route that seems frozen in time.

Climbing from Tovena (Cison di Valmarino, TV) or descending from Mel (BL), the bends tighten, the rock walls close in, and brief glimpses of the valleys below open up at every turn. In spring and autumn the colours of the woodland make the route even more evocative. The pass is also a classic destination for cyclists and motorcycle enthusiasts, thanks to its technically demanding hairpins set against strikingly beautiful scenery.