Why Are Those Stones So Perfectly Square? Somebody Cut Every Face

The stone is worked so that every face that will be visible or in contact is flat, square to its neighbours and cut to a planned dimension, which means each block is measured, marked and dressed individually with chisels before it goes anywhere near the wall. Blocks are then laid in courses of even height with joints only a few millimetres thick, since the faces meet so accurately that little mortar is needed. That accuracy is the whole point and the whole cost, since dressing a face by hand takes a mason hours and the material removed is wasted.

The advantages over roughly shaped stone are structural as well as visual:

• •Load spreads evenly across a full flat bed rather than on high points
• •Thin joints mean less mortar, which is the weakest part of any wall
• •Water finds fewer routes in, so frost damage is reduced
• •Walls can be thinner for the same strength
• •Openings and arches can be set out precisely
• •The finished surface announces what was spent

Almost no large building is solid dressed stone throughout, and understanding the construction explains a great deal about ruins. The usual arrangement is a facing of dressed blocks on the outside, a second facing on the inside, and a core between them filled with rubble and mortar, which uses the expensive material only where it shows and does the bulk with whatever is cheap. That works well while the facings are intact and fails badly once they are breached, since the core has little strength of its own and washes out. Robbing the dressed facing for reuse is also the commonest fate of an abandoned building, which is why ruins frequently show a rubble core with the good stone gone.

Most walls are not built this way and the alternatives form a recognisable ladder. Random rubble uses stone as it comes, fitted together with whatever mortar is needed and no courses at all. Coursed rubble squares the stones roughly so they sit in rough horizontal bands. Squared rubble dresses the faces but not to fine tolerance. Each step up costs more mason time and gives thinner joints and a more regular appearance. Many buildings use several grades on the same elevation, with the finest work around doors and windows and at the corners where accuracy matters structurally, and rougher work across the plain wall between.

The visible face is worked to a chosen texture rather than simply being flat, and the choice is a deliberate part of the design. A smooth rubbed face gives the plainest and most formal appearance. Tooled finishes leave regular chisel marks running in one direction, and the pattern and spacing vary by period and region enough to help date a building. A deliberately rough raised face within a chamfered border, called rustication, gives a heavy fortified appearance and was used on the lower storeys of Renaissance palaces specifically for that effect. The finish also affects weathering, since a rough surface holds water and a smooth one sheds it.

Dressing every face flat and square lets blocks be laid in courses with joints a few millimetres thick, which spreads load evenly, minimises the mortar that is the weakest part of a wall and keeps water out. The cost is hours of a mason's time per block, so most buildings use it as a facing over a rubble core, which is why robbed ruins show the core with the good stone gone.