Currently developing a system whereby disparate bands meet seasonally at gathering grounds to share knowledge, settle disputes, propose marriages (like the Icelandic Althing). Sites known to people get used over and over, with structures being maintained or falling into permanent ruin for later societies to find.
This, too, is a generic concept - "sites" are interesting places that people can discover and can share knowledge of with each other. for now it's these gathering places, but as the ages (and game dev) progress, a "site" might take all different sorts of forms and be shared for any number of reasons. I would imagine that later on, gold prospectors will use the same generic mechanism to share or sell valuable knowledge of gold veins. Fully emergent gold rushes should be a thing or else I've failed.
