The Geology Shapes the Method
Ligurian dry-stone construction developed with the materials at hand. The hillsides above the coast expose primarily three rock types: Ligurian ophiolites (greenstone, serpentinite, and related metamorphic rocks) in the western and central parts of the region; grey Ligurian limestone in the Alpi Liguri; and the sandstone and schist of the Macigno formation that runs through the eastern Ligurian Apennines toward La Spezia and the Cinque Terre.
Each of these behaves differently when worked and when loaded. Builders in any one locality knew the material of their immediate terrain and selected and placed stones according to those specific properties. What follows describes general principles as they apply across the region, with reference to the coastal schist and sandstone zones where most of the surviving terrace walls are concentrated.
Sorting a Stone Pile
Before any building begins, experienced builders sort the available material into categories. The categories are not rigid — they reflect judgements made on the day about what each piece can do — but in practice most builders think in terms of:
- Face stones — flat-fronted, with at least one square edge, wide enough to present a stable face and deep enough to reach well back into the wall core. In Ligurian schist this often means a piece 20–30 cm wide, 12–20 cm tall, and 20–35 cm deep.
- Through-stones (tie-stones) — long enough to span the full depth of the wall, or as close to it as available material allows. They are typically the largest pieces in the sort. Irregular shape matters less than length and stability.
- Hearting — angular fragments and smaller pieces used to fill voids in the core between the two faces. The critical quality is angularity: rounded stones in the hearting can shift and compact, which eventually causes the face to move. Angular pieces interlock and resist settlement.
- Coping stones — flat, wide pieces set aside specifically for the top course. These need to be heavy enough to resist displacement by frost or foot traffic and wide enough to span the top of the wall.
Reading a Stone Before Placing It
Each stone has a natural bed — the orientation in which it was deposited or formed. For sedimentary and metamorphic rocks (the majority in Liguria), this plane of stratification or foliation is also the plane of greatest strength. A stone placed with its bed horizontal and its face presented to the outside carries load along its natural grain rather than across it, and is far less likely to split under pressure.
Schist in particular tends to have a pronounced foliation that can make it seem like a naturally thin, flat stone. In reality, the cleavage faces are often not the strongest planes, and a piece of schist placed with its cleavage vertical — as a facing stone with the flat side out — may delaminate after a winter of frost. Correctly placed, it should be oriented so that the pressure of the wall above runs perpendicular to the foliation, not along it.
The Locking Stone
A recurring element in Ligurian wall construction is the use of small wedge-shaped fragments to stabilise a face stone that does not sit completely flat on the course below. Rather than allowing a gap or omitting the stone, the builder taps a wedge-shaped piece — a pinning stone — into the void until the face stone is secure. This is a technique that requires judgment: too tight a pin can lever the stone above out of position; too loose a pin will fall out over time.
Pinning stones are typically placed at the back of a face stone, out of sight, rather than at the front where they could be displaced by surface erosion or contact. Visible pins at the front of a wall face are usually a sign of hasty construction rather than a deliberate choice.
Corners and Returns
Where a terrace wall meets a path, a staircase cut into the slope, or another wall running at an angle, the corner requires careful treatment. The two wall faces must be interlocked at the corner rather than simply butted together; butted corners almost always separate in time under differential loading.
Interlocking a corner means alternating which wall's stones extend around the bend on successive courses: on one course, the stones of the main wall face wrap around to form the corner; on the next course, a stone from the return wall overlaps and locks the first. This alternating bond is the same principle that governs vertical joint staggering throughout the wall, applied in three dimensions.
Practical Notes for Restoration
When an existing wall section is repaired rather than built from scratch, the original stones are reused where possible. They have already been shaped by weathering to fit their former position and are unlikely to split unpredictably. Stones from collapsed sections are sorted before being relaid — face stones back to face positions, through-stones identified and set aside, hearting material separated from potential facing material.
New stone introduced into a repair should match the original material as closely as possible. Mixing rock types of significantly different hardness in the same section creates differential wear rates; the softer material erodes faster and the section that contained it loses stability faster than the surrounding original wall.