Which risk increases when laying Roman roads across areas high in organic matter like swamps?

💡 Explanation

When Roman roads were built over highly organic soils, lack of oxygen promotes anaerobic decomposition because microorganisms digest organic material without air, which releases gases and causes significant volume reduction leading to soil subsidence and uneven settling of the roadbed. Therefore anaerobic decomposition is the primary risk, rather than frost heave, sediment deposition, or vegetation which are less directly linked at this environment.

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