Which risk accelerated Roman fortified walls' collapse in coastal areas during the empire's decline?

💡 Explanation

When porous Roman concrete is exposed to salt water, capillary action draws saltwater into concrete pores where, upon evaporation, salt crystallization pressures cause expansion and cracking, weakening structure. Therefore efflorescence accelerates collapse, rather than thermal stress, sea level or seismic damage which depend on independent environmental dynamics.

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