Which structural vulnerability appeared earliest in Roman castra fortifications utilizing a vallum with timber palisade construction?

💡 Explanation

When projectiles ignited the timber pallisade, rapid pyrolysis released flammable gasses, accelerating the spread of flames leading to breaches because the wood acted as fuel. Therefore, ignition and fire was the initial problem faced, rather than effects such as hydrostatic pressure, cracking or settlement which require changes to the build material or longer durations.

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