At about half the wall’s height, the waller lays the throughs. These are long stones, long enough to reach right across the wall from one face to the other, and usually a little longer, so that they stick out an inch or two on each side. They tie the two faces together. Without them, the faces of a wall can slowly spread apart over the years, with the hearting slipping down between them, until the wall bellies out and falls. With them, each face is held to the other.
Throughs are set at intervals along the wall, usually about a yard apart, sometimes closer. On the hill wall, they are the gray stones you can see poking out a little from both sides at about the height of a walker’s waist. They need a flat, level course to sit on, so the course beneath them is finished carefully, with the hearting brought up level with the face stones. Each through is laid across, checked to see that it sits firm and does not rock, and then the gaps between the throughs are filled with ordinary face stones and hearting, bringing the whole course level again.
Not every wall uses throughs in the same way. In some places, the custom is to lay them in one row at half height; in others, there are two rows, one lower and one higher; and in some walls built with smaller stone, there are none at all, and the wall is held together by the batter and the hearting alone. The hill wall has one row, which is the common way where long stones are easy to find. Its builders found them in the slope above, where the rock splits naturally into long, flat pieces.
Above the throughs, the work goes on as before. The strings are moved up the frames. The courses are laid, one on two and two on one, with lengths into the wall and joints crossed, and the hearting packed behind each stone as soon as it is set. The batter carries on, so that the faces draw a little closer together with each course. The wall above the throughs is narrower than below, and the stones are smaller and lighter, and the work goes a little faster.
From time to time, the waller steps back. It is useful to see the wall from a few paces away, because things that cannot be seen from close up are obvious at a distance: a course that has started to dip, a stone that sticks out too far, a place where the face has drifted away from the string. Usually these are small things, fixed by lifting off a stone or two and setting them again. Occasionally a whole course comes off and goes back on. This does not take as long as it sounds.
There is a rhythm to it after a while. Pick up a stone, look at it, set it, check it for rocking, pack behind it, pick up the next. The heap on the grass gets smaller. The wall gets taller. Down below, the shadows of the trees along the forest edge move slowly across the field as the afternoon goes on.