This is really weird. When I was a lot younger and playing AC2 for the first time, I would notice Rooftop Archers would detect me a bunch, and while I'd still be able to assassinate them, it'd only be in that moment of shock/surprise as they're still yelling about seeing me. I didn't really care so much. A stealth kill was a stealth kill, regardless of whether the Animus thought they saw me for a moment before dying.
The thing is, Assassin's Creed doesn't have footstep sound factor into its Stealth, not until AC Unity/Syndicate, so generally speaking you can run and sprint behind enemies as much as you like.
I brought that up because I've been playing a bunch of AC2 again (Ezio Collection), and I tried to Fast Walk up behind a Rooftop Guard instead of Sprinting/Running at him. And this time he didn't hear me, didn't turn around, didn't see me. I assassinated him without issues.
Is this something people have knowledge of? It's odd for this to be an inconsistency when the rest of the game, and the rest of the series until Unity just does not work this way. I'm not really complaining or anything, I actually think it's pretty cool, but it's something that was never alluded to or explained in-game at all. I could just be literally seven years late on something everyone here knew about, but man, wow. Wow. In one sense it's logical to me; on the rooftops it's quieter than on street-level, so there's way less ambient noise for the Archer to get distracted with, or for your own footsteps to blend into. That's actually a super easy justification and makes the mechanic -- if indeed that's what it is -- feel actually thoughtful.
I've never thought about it being a mechanic like that in the early games. I have, however, always tried to move around quietly when there was a rooftop guard nearby, but that was just in the interest of roleplaying, or doing what would make sense to me.
Did you double check this to make sure it's actually the sound that they're responding to? Does it matter if you're running on flat, stone roofs or sloped roofs with tiles? Could be interesting to experiment with.
It's definitely the sound they're responding to. I imagine it's a built-in thing for rooftop archers to respond to someone running across the roof.
Yeah, I've run around a few more times and this all checks out. They can hear Ezio from surprisingly far away. Fast-Walking up to them or Ledge Assassinating them is the only way to get a true Stealth Kill. Also, something I hadn't noticed seven years ago, Notoriety only gets added if someone sees you before someone dies, even if it's the person being killed. As in, if a guard is eliminated with a True Stealth Kill (no momentary detection before the stab) you will not gain Notoriety for that assassination.