Which constraint primarily limited the height of Roman concrete fortifications, such as the Porta Nigra?

💡 Explanation

When Roman concrete fortifications gained height, settlement-induced tensile cracking risk grows because non-homogeneous soil consolidation creates differential stresses. Therefore settlement-induced tensile cracking was a primary constraint, rather than wind instability, geothermal stress, or tensile material failures, which were relatively lower risks for these structures.

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