Colle delle Finestre: The Gravel Sanctuary Where Froome's Solo Attack Turned the Race Around, Once a 300-Year-Old Military Fortress Road

A Road Built for a Military Fortress, Now a Gravel Sanctuary for Cyclists

In the early 18th century, the Duchy of Savoy built a winding military road through the high mountains on the border between Piedmont and France, designed to connect the valley with the Forte di Fenestrelle at the summit—a defensive complex touted as the longest in Europe. The road’s purpose was purely military: moving supplies, shifting troops, and crossing the watershed between the Susa Valley and the Val Chisone. More than three hundred years later, the fortress no longer serves any defensive role, but that gravel military road, born of war, has been given a new life in the 21st century by cycling—it has become one of the most dramatic climbs in the Giro d’Italia of the past two decades: the Colle delle Finestre.

If you need a single image to remember this mountain, it should be that afternoon on Stage 19 of the 2018 Giro d’Italia. British rider Chris Froome, mired in a difficult position in the general classification and facing what seemed like an insurmountable time gap to the leaders, launched an almost reckless long-range solo attack on the gravel section of the Colle delle Finestre. On that steep, jarring gravel climb, he dropped his rivals one by one, ultimately opening a massive gap of over three minutes on the stage, completely overturning the overall race situation and etching the Colle delle Finestre indelibly into the minds of cycling fans worldwide. That attack is widely regarded as one of the most iconic displays of individual heroism in Giro history of the past decade.

Route Basic Information

Different sources vary slightly on exact kilometer and gradient figures, and the summit elevation differs somewhat in some references. The numbers above are approximate values compiled from multiple sources; for actual conditions, please refer to roadside signage and GPS records.

Segment Breakdown: Two Worlds of Tarmac and Gravel

The most distinctive feature of the Colle delle Finestre is that it is almost split into two completely different worlds—the first 10.5 km is normal paved asphalt road, while the final 8 km is entirely unpaved gravel and compacted dirt. This “tarmac-then-gravel” design sets it apart from the vast majority of European mountain climbs.

First section (Susa to the gravel start, approximately 10.5 km): Setting off from the floor of the Susa Valley, the road climbs gently along the valley on standard asphalt, with relatively regular gradient changes, mostly falling between 7% and 9%. This stretch can be treated as a “warm-up and settling-in” phase, letting the body gradually adapt to the rhythm of continuous climbing, while also offering the best opportunity to admire the traditional Italian mountain villages of the Susa Valley—stone cottages, church spires, and terraced vineyards and orchards forming the quintessential pastoral landscape of the Piedmont mountains.

Gravel start to the middle section (approximately the first 4 km of gravel): The moment the asphalt ends, the road surface changes instantly. The mix of gravel and compacted earth, combined with a sustained gradient of around 9% to 10%, noticeably reduces the efficiency of power transfer—the same wattage output translates into significantly slower forward speed on gravel compared to asphalt, due to greatly increased rolling resistance. This section also offers the most open and dramatic views, as the trees gradually thin out and the road can be seen coiling up the bare mountainside in impossibly tight hairpin switchbacks, layer upon layer, looking from a distance like a giant spiral staircase.

Final section (core gravel to the summit, approximately 4 km): This is the hardest stretch of the entire climb. Sustained gravel surface, local gradients approaching 14%, and the altitude now nearing 2,000 meters, where thinner air begins to noticeably affect breathing efficiency, combine to push both physical and mental endurance to their limits here. Many riders who have climbed it mention that the biggest enemy on this stretch is often not the gradient itself, but the “sense of uncertainty” brought by the gravel surface—you never know whether the next pedal stroke will lose momentum due to a wheel slip. This constant focus drain is more mentally exhausting than a purely numerical gradient. Upon reaching the summit, the view opens up dramatically, with layered ridgelines of the Alps stretching into the distance. That sense of relief after a long battle on gravel, finally seeing flat ground, is the most direct reward the Colle delle Finestre offers every challenger.

Past and Present of a Three-Hundred-Year-Old Military Road

To truly understand the significance of the Colle delle Finestre, one must first appreciate the scale of the Forte di Fenestrelle beneath it. This defensive complex, built and expanded by the Duchy of Savoy between the late 17th and early 18th centuries, stretches layer upon layer along the mountain ridge and is claimed to be one of the longest walled defense systems in Europe, designed to guard the strategic border route between France and Italy. To allow troops and supplies to be moved up the mountain quickly, military engineers carved a zigzag military road into the steep mountainside, using a continuous series of tight hairpin bends to keep gradients within limits manageable for men and beasts of burden—which explains why riding the Colle delle Finestre today reveals such a high density of nearly spiral-stacked switchbacks. They were not designed for scenic effect but are a pure legacy of military engineering considerations.

As the European political landscape shifted, the fortress gradually lost its military value, and the road fell into years of obscurity, used only occasionally by local residents and hikers. It was not until the Giro d’Italia first included it in a stage in 2005 that the Colle delle Finestre returned to the world’s attention, and that final unpaved gravel section—never surfaced with asphalt—unexpectedly became its most distinctive hallmark. In an era when the vast majority of European mountain roads have been fully paved, such a climb retaining its original surface texture is exceptionally rare, giving it a fundamental distinction from purely speed-and-efficiency-oriented asphalt climbs.

Sensory Experience on the Mountain: From Pastoral Poetry to the Lunar Surface

The visual and sensory experience of the Colle delle Finestre undergoes a dramatic shift as the road transitions from asphalt to gravel, and this contrast is one of its most unforgettable qualities. The early asphalt section passes through typical Piedmont mountain villages of the Susa Valley, with stone houses scattered across gentle slopes, occasionally dotted with vineyards and orchards, the air carrying the characteristic dry herbal scent of mountain regions—an overall atmosphere that is relatively welcoming and pastoral.

But the moment the wheels touch the gravel surface, everything around seems to switch to an entirely different scene. Trees disappear rapidly, replaced by vast expanses of bare gray-white rock walls and earthen slopes, accompanied by the constant vibration of gravel under the wheels and the sound of tires grinding. Many riders who have been there describe the visual impact of this stretch as “riding on the surface of the moon” or “entering another planet.” The successive hairpin bends stack up in the distance like a giant spiral staircase piercing the clouds. This highly artificial yet desolate and majestic landscape is completely different from the natural rock peaks of the Dolomites, instead evoking a stark, martial aesthetic unique to wartime relics. Upon reaching the summit, the view opens up dramatically, overlooking the entire Susa Valley and the distant ridgelines of the Alps. That feeling of release after enduring the rough gravel road and finally seeing flat ground again is the most profound gift this mountain offers every challenger.

Power and Pacing Estimates: How the Physical Model Works

Because the Colle delle Finestre has distinctly different road surfaces on its lower and upper sections, we estimate it in two segments to make the numbers closer to real-world feel.

The standard physical model is as follows:

P = (Fg + Fr + Fa) × v ÷ drivetrain efficiency

Fg = m × g × sin(arctan(gradient))       gravitational component
Fr = m × g × cos(arctan(gradient)) × Crr   rolling resistance
Fa = 0.5 × ρ × CdA × v²                  aerodynamic drag

Overall estimate for the full climb (18.5 km, 1,694 m of elevation gain, 9.1% average gradient), assuming a uniform asphalt rolling resistance coefficient for the entire route:

• Total mass m = 70 kg rider + 9 kg bike and gear = 79 kg
• Gravitational acceleration g = 9.81 m/s²
• Rolling resistance coefficient Crr ≈ 0.005 (asphalt road tires; this is a simplified baseline value for the overall estimate)
• Drag area CdA ≈ 0.32 m² (seated climbing position)
• Air density ρ: decreases noticeably with altitude (roughly 480–2,178 m range)
• Drivetrain efficiency ≈ 0.975

Supplementary estimate for the gravel section (final ~8 km, ~1,000 m of elevation gain, rolling resistance coefficient raised to Crr≈0.010 to reflect the higher rolling resistance of gravel):

Looking at these two sets of numbers together is very revealing: on the gravel section, even when the gradient is similar to the asphalt section, the increase in rolling resistance alone (this estimate assumes gravel Crr is roughly double that of asphalt) is enough to cause a noticeable drop in average speed at the same power output. These are physical-model estimates that do not account for additional variables from rider skill differences on gravel (such as tire choice or weight distribution), so the actual gap could be even larger. Use them only as planning reference.

On the pro record: At Stage 19 of the 2018 Giro d’Italia, Froome’s solo attack on the Finestre gravel section was widely reported as the key turning point that opened a gap of more than three minutes, ultimately helping him overturn the overall race situation and take that year’s title. In 2025, the Colle delle Finestre was designated the Cima Coppi (the race’s highest point, named after legendary rider Fausto Coppi) for that edition, where Simon Yates delivered a classic comeback victory. Because weather, group tactics, and gravel road conditions (whether it has been graded and maintained) vary enormously between editions, pro riders’ actual climbing times are not directly comparable to a recreational rider’s personal effort, so no precise figures are cited here.

A Taiwanese Rider’s Perspective: Translating to Your Ability

Taiwanese road cyclists are relatively unfamiliar with mixed terrain like “gravel climbing”—classic climbs such as Wuling, Fengguizui, and Beiyi are almost entirely on well-paved asphalt. The final 8 km of gravel on the Colle delle Finestre is closer in feel to the gravel conditions of some Taiwanese forest roads or farm access roads, except that both the gradient and elevation are far beyond what most people are used to. If you have no gravel riding experience at all, it is strongly recommended that you first find a forest road or gravel path in Taiwan with similar conditions for adaptation practice before considering taking on the Finestre.

Practical planning reminders (general guidelines only; for actual planning, please refer to the latest official announcements and local information):

• Tire choice: This is the most critical equipment decision on the Colle delle Finestre. Narrow pure-road tires will suffer significantly in grip and comfort on the gravel section. Most experienced riders choose slightly wider tires (e.g., 28c to 32c) with tread patterns better suited to gravel, balancing efficiency on asphalt with grip on gravel.
• Season: The pass sits at high altitude and is closed in winter. The open period is concentrated from summer to early autumn. Be sure to check the road’s open status for the current year before departing.
• Altitude adaptation: The summit approaches 2,200 m. If your usual training environment is near sea level, plan one to two days of buffer for acclimatization.
• Getting there and back: Most riders use Turin (Torino) as their base. For actual car rental and transfer arrangements, please check through official local channels; no specific prices or schedules are listed here.

Gravel Pacing and Riding Technique: A Completely Different Logic from Asphalt

On gravel sections, both pacing and bike-handling logic must be separated from asphalt-climbing thinking. First is body position and weight distribution: grip on gravel is far lower than on asphalt, and aggressive out-of-the-saddle surges can easily cause the rear wheel to spin and slip, wasting precious energy and risking loss of control. Most experienced gravel riders recommend staying seated as much as possible, keeping steady vertical load on the rear wheel, and minimizing lateral sway.

Second is line choice: gravel surfaces are not uniformly loose. There are usually compacted “hard lines” from tire ruts alongside loose, piled gravel. Experienced riders try to follow the compacted ruts and avoid obviously loose or deeply piled gravel areas, which can significantly reduce rolling resistance and the risk of slipping.

For energy management, since rolling resistance on gravel is inherently higher, it is advisable to dial back your pacing target on the asphalt section slightly and save more mental and physical reserves for the gravel—if you discover you are already half-spent once you hit the gravel, the rest of the experience will be very grueling.

Equipment Details: Full Adjustments from Tires to Gearing

Beyond the tire choice mentioned earlier, the Colle delle Finestre demands a more comprehensive approach to overall bike setup than most riders imagine. On gearing, given that rolling resistance is already high on gravel and the final section’s gradient approaches 14% locally, it is advisable to prepare a lower lowest gear than you would use for a typical asphalt climb, allowing you to maintain a steady cadence on the gravel rather than being forced to muscle through—if your cadence drops too low on gravel, uneven torque delivery actually makes slipping more likely.

On frame and bike type, in recent years many riders choose a gravel bike or an endurance road bike with wider tires to take on the Finestre. These bikes typically offer greater tire clearance and more stable geometry, boosting handling confidence on the gravel. If you insist on using a pure race bike, pay extra attention to the limits of tire width and pressure adjustment.

Also worth noting is the bike’s carrying system: the constant vibration on the gravel section is a major test of how securely bottle cages, tool bags, and other accessories are mounted. Check that everything is firmly tightened before departure to avoid items shaking loose and falling off mid-ride.

Safety Reminder: The Dual Risks of Gravel and High Altitude

Risk of Losing Control on Gravel Surfaces: Whether climbing or descending, gravel surfaces offer far less grip than asphalt, especially when cornering and braking on descents, where stopping distances increase noticeably. Be sure to significantly reduce your speed and brake early to avoid sliding off the road when entering hairpin turns too fast.

Tires and Mechanical Failures: Gravel surfaces place higher demands on tire puncture resistance. It is recommended to carry enough spare tubes and repair tools, and to consider using puncture-resistant inner tubes or a tubeless system to reduce the risk of flats. If you get a puncture on remote mountain gravel sections, the wait for assistance can be very long.

High-Altitude Reactions: The summit of the pass approaches 2,200 meters. If you experience unusual headaches, nausea, extreme fatigue, or other symptoms, stop climbing immediately and consider descending as appropriate. These are warning signs to watch for; this article’s advice cannot replace professional medical evaluation.

Sudden Weather Changes: Weather at high-altitude gravel passes can change just as quickly. In the afternoon, fog or rain is common in the mountains. Wet gravel combined with limited visibility significantly increases risk, so try to schedule your climb for the morning hours.

Hypothermia on Descents: Temperatures at the summit can be noticeably lower than in the valley, and while speed is limited on gravel descents, the wind chill effect should not be underestimated. It is recommended to carry a lightweight windproof layer to cope with the temperature difference.

Beyond the Susa Valley: Another Way to Connect with the Chisone Valley

Most riders tackle the Colle delle Finestre from the Susa side, but the other end of this pass connects to the Chisone Valley, offering the option of planning a point-to-point route rather than simply going up and back the same way. If time and logistics allow, climbing from the Susa side and descending into the Chisone Valley makes the whole ride more complete while avoiding the jarring experience of repeating the same gravel descent. However, road conditions, gradients, and the proportion of gravel on the Chisone Valley side differ from the Susa side. Before planning, be sure to check the latest road condition reports and assess your own ability to handle an unfamiliar descent.

Why the Gravel Sanctuary Is Worth a Pilgrimage

What makes the Colle delle Finestre unique is that it satisfies two very different cycling desires at once—riders craving a pure climbing endurance test can find their familiar rhythm on the first 10.5 kilometers of asphalt, while those seeking a gravel challenge can experience something close to a “one-day monument” feel on the final 8 kilometers, pedaling the legendary surface where Froome rewrote the race’s outcome. This mixed-terrain design has also made it an increasingly popular new pilgrimage destination among European riders amid the global gravel cycling boom in recent years.

In recent years, as the gravel cycling trend continues to heat up worldwide, the Colle delle Finestre has evolved from simply being a “classic Giro d’Italia stage” into a shared pilgrimage landmark for “asphalt-and-gravel crossover enthusiasts.” Many riders who previously only rode pure road bikes have, because of this pass, seriously encountered the fun and challenge of gravel riding for the first time. This crossover appeal is a major reason its popularity keeps rising.

For Taiwanese riders, the Colle delle Finestre may require more preparation than a typical asphalt climb—appropriate tire choices, practicing gravel riding techniques, and even mentally adapting to “uncertain surfaces.” But this extra preparation is precisely what sets it apart from other legendary climbs. When you finally stand at the 2,178-meter summit and look back at the winding road that alternates between gravel and asphalt, the sense of accomplishment is completely different from any pure asphalt climb.

Key Takeaways

• The Colle delle Finestre is approximately 18.5 kilometers long: the first 10.5 kilometers are asphalt and the final 8 kilometers are unpaved gravel, with a total elevation gain of about 1,694 meters and an average gradient of 9.1%
• In the 2018 Giro d’Italia, Froome launched a long-range solo attack here to turn the race around; in 2025, it became that edition’s Cima Coppi
• Based on a physical model estimate, a typical enthusiast (2.5 W/kg) would take about 2 hours 1 minute for the entire climb; due to higher rolling resistance on the gravel section, average speed at the same power is noticeably lower than on the asphalt section
• Tire choice is critical to success; it is recommended to use slightly wider tires suited for gravel and to build up gravel riding experience beforehand
• Grip on gravel sections is far lower than on asphalt; reduce speed and brake early on both climbs and descents, while also watching for high-altitude and sudden weather risks

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