White cliffs undercut by waves so severely that medieval buildings teeter on the edge; slowly tilting toward the sea.
Carsten Steger, CC BY-SA 4.0, via Wikimedia Commons
A Foundation of Ancient Seabeds
The white cliffs of Bonifacio rise up to 70 meters above the Strait of Bonifacio. These are not granite, like much of Corsica and neighboring Sardinia, but a younger limestone. The rock, a type of calcarenite, formed from marine sediments deposited during the Miocene Epoch, roughly 16 to 21 million years ago. Geologists refer to this layer as the Bonifacio Formation.
This formation contains many fossilized remains of marine life from a temperate, shallow sea. The primary components are the skeletons of bryozoans, red algae, foraminifers, and echinids. These organisms formed extensive bioclastic sand dunes on the sea floor. Tectonic forces later uplifted this entire seabed, exposing the soft, porous limestone to the elements. The town of Bonifacio, established in the 9th century, is on this Miocene foundation, a vertical slice of a prehistoric marine ecosystem.
A Drowned Valley Undercut by Waves
The dramatic coastal geomorphology is the result of two distinct processes. First, the harbor itself is a ria, a drowned river valley. During past ice ages, when sea levels were lower, a river carved a steep canyon through the limestone. As the ice sheets melted and sea levels rose, the ocean flooded the canyon, creating the narrow, fjord-like inlet that shelters Bonifacio's port.
The second process is ongoing and relentless: wave erosion. The constant force of the sea carves away at the base of the porous limestone cliffs. This creates a deep notch or undercut, leaving the rock above unsupported. This process is especially pronounced along this stretch of coastline, which is considered highly sensitive to erosion. Eventually, the overhanging rock collapses in large sections. This slow, persistent undercutting is why the medieval buildings constructed on the very edge of the precipice appear to lean out over the water, with some at risk of eventually falling into the sea.
💡Fun Facts
The King of Aragon's Stairway is a set of 187 steps carved into the cliff face at a steep 45-degree angle.
Legend claims the stairs were cut in a single night during a siege in 1420, but they were actually created by monks to access a freshwater well.
The natural harbor is so well-protected that some historians believe it is the port described in Homer's Odyssey as the home of the giant, cannibalistic Laestrygonians.
The limestone cliffs are part of the Bouches de Bonifacio Nature Reserve, an international marine park established by France and Italy in 1993.
The cliffs and town are always accessible. The King of Aragon's Stairway is open daily from April to October, with hours typically from 9:00 AM to 7:00 PM, but times can vary.
Admission
Walking through the town and along the cliff paths is free. Admission to climb the King of Aragon's Stairway is €3.50 for adults.
Accessibility
The old town has steep, narrow cobblestone streets. The paths along the clifftops are unpaved. The King of Aragon's Stairway is extremely steep and physically demanding.
