If I have 6000 and stealth i'm to draw them into the nearest valley and use archers to catch them in a crossfire (i'd have a vanguard protect them)from the high ground. During this I would have a small force face them from the front while the larger force utilized stealth to move into the back. Using their inevitable panic upon being surrounded I send cavalry (If I have any) in small spearheads to break up any formations and to take out any officers trying to regain control of their troops. The rest of the battle would simply utilized basic ground troops to pin them in the valley while having the cavalry heard them making the volleys or arrows more effective.
(I know very little about the Roman military strategy so this was what I came up with).
Caption this Meme
