That sounds inherently unsafe to me. The original texts were often biased by whatever agenda the person writing them was trying to forward, then we've got yet another layer of bias and selective interpretation from someone who wasn't there, and wasn't even a contemporary in a lot of cases.
Now I'm not saying this is reason to simply toss them out, but I'm rather dubious at classifying them as primary sources. Why would an ancient historian, writing from an older source be considered primary, yet a modern historian writing from the same older source be secondary? At least the latter is going to have some degree of authenticity in mind, and will have peers ready to jump on the slightest inaccuracy and bias.
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