It's one of those Early Access games on Steam. So far, not a lot in terms of single player, but lots of fun to be had in building.
No battalions yet.
But crazy stuff like building this thing:
Some people have built transforming creations, helicopters (https://www.youtube.com/watch?v=kfldluO4nhU), and then there are the NSFW ones: http://kotaku.com/the-nsfw-creations-of-besiege-players-1685002022
Besiege is a physics based building game in which you construct medieval siege engines and lay waste to immense fortresses and peaceful hamlets. Build a machine which can crush windmills, wipe out battalions of brave soldiers and transport valuable resources, defending your creation against cannons, archers and whatever else the desperate enemies have at their disposal. Create a trundling behemoth, or take clumsily to the skies, and cause carnage in fully destructible environments. Ultimately, you must conquer every Kingdom by crippling their castles and killing their men and livestock, in as creative or clinical a manner as possible!
No battalions yet.
But crazy stuff like building this thing:

Some people have built transforming creations, helicopters (https://www.youtube.com/watch?v=kfldluO4nhU), and then there are the NSFW ones: http://kotaku.com/the-nsfw-creations-of-besiege-players-1685002022