We’ve all seen sketches of long lines of Egyptian slaves pulling huge blocks of stone on rollers, or up ramps, to form the pyramids. For me, and perhaps for many of my readers, that’s the dominant image when I try to picture how anyone built with stone in the past. I know that sometimes, stone was carried by boat across the English Channel or farther, in the Middle Ages, and I automatically picture huge blocks like that. But no, that’s not how it was. Some videos by an American stone mason who visited a few castles helped me get it really straight in my imagination.
Medieval castles used two kinds of stone: field stones of various kinds, picked up locally in the fields, and quarry stone that may have been transported a little distance. The cut/dressed stones brought from a quarry were clearly more expensive than local field stone, so they were used sparingly for specific tasks. Quarry stones were usually limestone, which was soft enough to carve fairly easily. A lot of limestone was shipped from Caen, in Normandy. The field stones, on the other hand, might be difficult to carve, so they probably weren’t cut.
Mike Haduck, the American stone mason, demonstrates how stones might have been sorted by natural shape in this video. Stones with a natural flat face went into one pile, while those with natural right angles went into another. Irregular and irredeemably round stones went into a third. Stones could then be shaped a bit and improved with hammer and chisel, so that the builder had a supply of flat-faced, roughly square blocks and rounded or irregular ones.
Flat-faced stones became facing-stones, the ones we see on the surface of the wall. A castle’s wall might be six feet thick. Each wall of flat-faced stones could only account for maybe 12 inches on each side, leaving four feet to fill in with irregular and round stones. Medieval masons used lime, sand, and water to make mortar. When the outer facing walls were a few blocks high, they started making layers of stones and mortar to fill in the middle section. The walls slowly rose like this, facing walls first, then fill. The facing stones were not usually all the same size, so their rows are only approximate.
Basically, if you wanted your facing stones to be all the same size, you were looking at thousands of quarry-cut stones, and the expense was much higher. If you wanted facing stones to be rectangular but it was okay if the masons used various sizes to level up their rows, it was a bit less expensive. If you didn’t mind using plain fieldstone for the walls, all pebbly and irregular, the cost was lowest.
King Edward I built seven castles in Wales at the same time, so some of them show cost-cutting stonework. At Harlech, you can see that squared-off facing stones cover the barbican towers, but the ordinary castle walls are pebbly fieldstone. It’s local stone, mostly sandstone. Even in the towers, the facing stones aren’t very regular. In a word, it was a cut-costs castle. We see the same fieldstone walls at Conwy Castle, built at the same time. By contrast, the royal castle at Caernarvon had fairly regular facing blocks in its ordinary walls.
Did kings cheap out? You bet. Next, let’s look at how they built holes into stone walls: arrow slits and windows.