Question about rivers and getting to the other side

[kmkenpo]

First off... I still have not purchased this game as of yet, but I am hoping to do so around Christmas or the New Year. None the less, I may have a question that is blaringly obvious, and for that, I am sorry.

As I have watched some Let's Plays I have noticed that the maps often come with rivers that do not allow passage. There seems to be an ocassional bridge scattered around the maps, as well as the possibility to get troops that can traverse those waters, or research spells that allow access. There even seems to be the cold weather affecting those rivers from time to time, which I think is pretty nice, but I am not sure if all rivers get this effect.

Question:
Is there a way to "build" a bridge... similar to building a fort, labratory and so forth? It would seem to me that if a group of humans, or lizards, or talking apes can build a fort, research magic, and spread the faith of a pretender, then certainly they could figure out how to tie some logs together make some sort of bridge or boat-like transport.

As I said, if this is a common question or something that is obviously already in the game, I do apologize. It has always just struck me a kind of weird... if not somewhat... lacking(?).

[kmkenpo]

Wow... it would seem that if I had simply taken the effort to use that stinking "search" bar right next to the "start a new discussion" button, I would have come across a few recent threads about this very topic. My bad :(

[Swirler]

Nah bridges are just randomly spawned upon map creation. Although I must admit it would be really nice to be able to build them.

Incidentally there's a few units who can naturally move across rivers;
Amphibians
Poor amphibians
River crossing
flyers (wings yo)

And if there is cold on both sides of the river normal units may move across it as well.