The photo below shows the construction of an arch culvert. Notice the use of the “stiff leg derrick” to lift the large stones into place. You can also see the wooden arch built to hold the large stones in place, while the mortar dried between the stones. The wooden structure was called the “falsewood”. Carpenters would have to construct the “falsewood” first from large timbers to hold the massive weight of the arch. At times, the large timber poles of the stiff leg derrick would snap or crack and have to be replaced.

Stone arch culvert bridges were constructed by building the abutments and wingwalls, then erecting a wood, arch shaped form, known as “centering”, on which the arch ring blocks of stone (keystone), spandrel walls and the parapet stones were put into place.