The development of fast-moving reliable tanks led to many ideas of how to slow or destroy them. Large shaped blocks of concrete, strengthened with a steel core, often called Dragon's Teeth were a good way to block a vehicle's progress.
 
Equally, infantry had to be stopped or channeled away, so engineers on all sides were kept busy constructing wooden and steel frames that held long rolls of taught barbed wire, solid enough to keep away all but the most determined men.
 
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