Forging one of the wedges for a Lewis. A lewis is inserted into a dovetailed recess is cut into the top of the stone block (mortise). The two outer pieces of the lewis device are inserted first and then spread by the insertion of a appropriate sized centerpiece. The three parts are then bolted together, a metal ring or shackle is attached and the block is hoisted by hook, rope and pulley. By this means, the block is gripped securely and appropriately balanced. Once set in its place in the structure, the lewis is removed leaving the upper surface smooth with no clamp or chains on the outside to interfere with the laying of the adjacent or next course of stones.
Stones with the mortised cavity for the insertion of a lewis have been found in England in Hadrian's Wall built c. 121-127 CE. Archaeologists have found further evidence of its use by the Saxons in England in buildings constructed in the 7th century.
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