Cathedral of the Assumption, Monreale, Sicily
Lamech is a descendant of Cain who appears in Genesis 4:18-24, where he tells his wives, "I have slain a man to the wounding of myself, and a stripling to my own bruising." Medieval exegetes believed that the slain man was Cain, that Lamech at the time was blind and had to be guided by his son when hunting, and that when he realized what he had done he killed the child for misguiding him. Following that tradition, the mosaic shows the boy directing blind Lamech's shot and the arrow piercing Cain's breast. The inscription also follows the medieval tradition: trahens lamec arcu suo interfecit caym, "Drawing his bow, Lamech killed Cain."
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View other panels in the cathedral's Genesis sequence.
Also see this mosaic of Lamech in the Palatine Chapel, Palermo.
Photographed at the cathedral by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.