How far could the legions travel in a day

[Carlton Bach]

I wonder if they had slaves whose sole purpose was to count their footsteps so distance could be judged on the march? Seriously. In a bizarre way it kind of makes sense.

That was the standard way of doing it. I wonder, though, whether they would have used slaves in the army. The skill to do this accurately was quite highly prized in the ancient world. I could see an agrimensor being proud of his ability.