It was made up by courts. In property and contract law, we still refer to some English cases. The statutes have either incorporated such concepts, or remained silent. In some situations, statutes have clearly reversed the common law, such as in absolute legal tort liability, in certain situations. A finding of negligence for example, per the statutes, is no longer necessary, in some factual patterns.
Precedents, standards and customs of the time and place were recognized by the courts.