Which risk increased during siege combat when Roman legionaries undermined enemy fortification walls with tunnels?

💡 Explanation

When Roman legionaries tunnelled under enemy walls, ground instability occurs due to subsurface material removal causing structural weakening and cave-ins trapping tunneling legionaries. Therefore, tunnelling collapses is the increased risk, rather than artillery inaccuracy, catapult weakening, or disease spread needing different specific conditions.

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