Pair bonding of course predates civilization, but I would consider any tribe that is advanced enough to give recognition of it as a marriage is civilization.
It's the difference between a tribe member thinking "I want to mate with Klinda, but she is mating with Urka already, and Urka is bigger than me. I'll find someone else.", or thinking "I want to mate with Klinda, but she is mating with Urka already, and the chief said that is good. I'll find someone else for the chief to call us good.".
It may not be very advanced, but at that point, the tribe members are acting in a civil manner. They don't have to build the Acropolis for it to be civilization.