This is the second time I fought a colossus - actually the same one. You see, I didn't save after killing him the first time, and when the High Priest said to go to the ocean and talk to a god, and "Simply give yourself to oceans" ... When the god didn't respond, I jumped in the ocean and discovered *I couldn't climb back out*.
So I had to reload and find the colossus again. This time I threw a bunch of adamantine weapons at him. The best part was when the spinning crossbow lopped off a limb. Them things must be sharp!