[lstodd]

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 back. No fancy shoes, no prep but for a hat and couple bottles of water. After a third walk or so it isn't even exhausting.

[watutalkinbout]

Sure, but I'd imagine the average human could walk substantially further on flat modern roads in modern footwear than on cobblestone with ancient sandles.

You use 10–20% more energy for just mildly uneven surfaces - probably more for roman cobblestone.

[lstodd]

Actually no. Uniform flat surface is tiring compared to a trail even in best shoes. Try walking 10 km on hardtop then compare to walking same distance on unpaved road.

For shoes we also went not too far: Merrel sandals basically replicate roman caliga with modern materials. And it's not like you can use even halfboots in mediterannean unless it's winter - it's just too hot.

[watutalkinbout]

Empirically, yes.

You seem to be equating flatness with surface hardness. Tarmac isn't unforgiving to walk on because it's flat, it's because it has no give.