Why we don\'t know so much about the roman Army?

[TITVS SABATINVS AQVILIVS]

Why, after all, we don't know so much (or at least, not how much we'd like to know...) about the roman Army?<br>
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Where are those accurate military manuals, we can expect from a people like the Romans?<br>
If I'm not wrong, Polibius gave us examples that suggest to us that everything was strictly codified...<br>
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I can guess those manuals were made and written in a lot of copies (besides I guess it was normal that any legion could have several of them for instruction and officers' consultation). Is it possible that none of those hundreds and hundreds of copies did not come to us?<br>
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So, were they ignored on purpose in the medieval transcriptions to avoid that other armies or powers could learn too much from such excellent guides, or what?<br>
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Ualete<br>
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Titus Sabatinus Aquilius<br>
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