Yeah, and the punishment for adultery is stoning. If you're reading Romans 13 properly, then Christ was wrong, and should have let the woman who committed adultery be stoned.
“If a man commits adultery with his neighbor’s wife, both the man and the woman who have committed adultery must be put to death." Leviticus 20:10.
Leviticus is from the Old Testament. My (basic) understanding is that the Old Testament was written by Hebrews and the New Testament by Christians. Perhaps someone can better explain it to me but my take is that moral code is only to be taken from the New. It seems the Old set the foundation for Christ to guide humans away from the evil that was plaguing the world before him.