Just got attacked by a Bronze Colossus.
It waltzed over all my weapon traps taking negligible damage, then spent several minutes chasing a peahen around my courtyard (and then demolishing some buildings after it had killed it).
I activated all my militia and stationed them at the far end of the entrance corridor behind the second set of traps. And waited, while the colossus stood around doing nothing for several minutes.
Eventually, one of my recruits decided to run outside to pick up some equipment from next to the colossus, who woke from whatever metalic daydream it was having, killed him, and then charged into my fortress.
It got past my traps with minor injuries, whereapon my militia zerg-rushed it.
Early in the fight, the colossus managed to KO my longsword-wielding cook, but after that was barely able to even hit anyone, let alone wound them. Meanwhile, my dwarves layed into it with enthusiasm, with my two marksdorfs causing several fractures by shooting at it; one of my axedorfs attempting to bite it in the head several times, and everyone else just whaling on it until they had broken off both its arms and one of it's feet.
And then continuing to hack, bash, kick, punch, and bite it for several minutes as it lay on the floor, until one of my hammerdwarves hit it in the lower body so hard that it flew off in an arc.
(Regretably, my longsword/cook died shortly after of suffocation before anyone could treat him).
The statue that was left behind was of two leopards, which makes for quite a mind-screw when trying to envisage exactly what the colossus looked like.