I think the answer is "artifact."
A man-made object is called an "artifact." Usually when this word is used, we are referring to an object that was used in an ancient culture, and was recovered during an archaeological dig. Some examples are:
- stone tools
- metal weapons
Artifacts help archaeologists learn a lot about about older civilizations, because they provide clues about how the people in this culture lived.
Natural objects, like rocks or plants, are not artifacts. Also, artifacts are usually small, portable objects -- so for instance, a road wouldn't be called an artifact.