There are two styles of walls "opus reticulatum," now used by everybody and the ancient style called "opus incertum." Of these, the reticulatum looks better, but its construction makes it likely to crack... On the other hand, in the opus incertum, the rubble lying in courses and imbricated, makes a wall which though not beautiful, is stronger.
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Chapter VIII "Methods of Building Walls" Sec. 1Vitruvius
Vitruvius
Vitter, David
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