I have noticed that much of the tactics of the Classical and Roman world died out. Roman legions and Greek hoplites switched with footmen and knights, and grandiose columns and greco-roman design became mottle and daub and Germanic(?) stone castles. Tunics were still around, for a time, but were replaced with different clothing. Temples and other such buildings became Christian-style churches.
Now, I may be completely wrong on everything here, but I was wondering if these styles in dress, combat and architecture were replaced during the Dark Ages. If so, then why? I wanted to ask what replaced the uniforms of the Roman legionnaires with knight's armour and the clothes of footmen and peasant-soldiers. So essentially: Why all this change? How did it change?
Another important question was, "Who would win, a Roman legion or a high-medieval army?"