The inspiration for the climbing in Assassin's Creed was... The Bourne Identity?
I was watching the Bourne Identity earlier and there's this scene where Jason is on the run from these army guys so he runs out of an old emergency exit which brings him to a high platform on an old building. His first thought is to try to climb up, but he drops his bag, so he decides to climb below the ladder but the ladder is old and doesn't go all the way down, and just as the army guys breach the door, he grabs ahold of the square shaped indent in the wall and shimmys against it. The army guys don't see him there so they go back inside and since there are no footholds directly down, he shimmies around the building to the next hand hold and keeps dropping down that way almost EXACTLY like you would in AC and especially AC2. I'll try to see if the particular scene is on Youtube, but anyone who watched the movie more than likely knows what I'm talking about.
Been a while since I've seen the movie, but this makes me have to check the scene out again.
https://youtu.be/GGuveoxVXaI here's the scene. It's towards the latter half of the video, at 2:20, but I'd watch the whole scene for context.
Movie is amazing, one of my favourites.
I think the climbing is not such much direct inspiration as it is a representation of moving through space in unexpected ways, i.e. all that parkour is about!
Man, Matt Damon looks so young in that. There is 14 years of gap between Identity and Jason Bourne though, so it's a given. The scene reminds me of the tight sequences Ezio has to go through in the Lairs of Romulus, especially since the camera is fixed and there isn't a lot of freedom in the motion, much like how Bourne can't simply drop down from the indent, lest he break his legs.