Has anyone else seen the alternate seige tower?

[chillinin]

I joined a seige led by an AI character in my faction, and when I joined the seige, I noticed that the seige towers were different. Instead of the three ladders, they had log ramps up to the top. They seemed much more effective, our troops were able to pile on the walls much more quickly. Has anyone else seen this? It doesn't seem to be a perk.

 

[enemy_man]

I've seen it once or twice. Maybe it depends on the map?

 

[Blood Gryphon]

They are for level 1 walls, you'll normally get the three ladder ones for level 2 and 3 walls. Depends on the map as well.