But so is more stone. You have to build bridges, etc.
Yes, stone is more available in the mountains. THat's true in reality,
and people carried it far away to build roads with. All we need to do is
hit the level where it's worth it, but still hard.
If we achieve a level where there is an interstate system with roads to
every city and so forth, we blew it. Major roads in medieval and ancient
times were rare... and a BIG deal, in terms of effort and their effect on
the cities they connected.