It's 10km, which is a lot more than 10k steps.
Walking on flat, paved surfaces, I do about 1850 steps per mile of distance[1]. I have a pretty long inseam, so I'm not surprised that I'd be under 1000 paces. Given that roads weren't paved with concrete or asphalt until relatively recently, I'm not surprised that the Roman mile is a little shorter than our current one[2].
[0] https://en.wikipedia.org/wiki/Mile#Name
[1] Garmin watch