Earlier quoted context omitted.
Cobblestones aren't walk friendly.
Asphalt/concrete isn't either. Gravel or packed dirt is way better. That said 30km/day is very real, even in mountain country. It takes 6-7 hours, the rest is resting/gawking/laying on a mountain watching the sky (or trying furiosly to find that effin trail on osmand). I walked that a few times a week when I lived in Montenegro, and that was 50/50 roads and mountain trails from sea level up to 700m-ish elevation and…
You use 10–20% more energy for just mildly uneven surfaces - probably more for roman cobblestone.