I've managed to build a bridge across a river, using a couple of rocks for additional support. It's wide enough to pull a cart over, and tall enough to sail a boat under.

I used core wood for the bulk of supports, and I have built a small outpost up one end.

I did this without using any cheats. I am using mods, but none that have any effect on building.

The bridge/outpost isn't pretty, but it works as intended.

https://steamcommunity.com/sharedfiles/filedetails/?id=2624229278

https://steamcommunity.com/sharedfiles/filedetails/?id=2624230091

https://steamcommunity.com/sharedfiles/filedetails/?id=2624230586