Which structural deformation in Roman castra earthen ramparts increased risk when besieging forces tunneled beneath?

💡 Explanation

When besieged forces tunneled, creep from compaction under load occurred because the earthen ramparts slowly deformed due to added stress from the removed material underneath, increasing the risk of collapse. Therefore, creep resulted, rather than thrust, shear, or heave which require different environmental conditions and geological vulnerabilities.

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