Roman property law was the most sophisticated system for organizing the ownership and transfer of things that the ancient world produced, and it is the foundation on which most modern property law in continental Europe and its legal descendants directly rests. The Roman jurists who developed it between the second century BC and the third century AD were not theorizing for its own sake; they were solving practical problems generated by the increasing complexity of a commercial economy that operated across thousands of kilometers and involved millions of transactions. The solutions they developed were elegant enough that Justinian’s sixth-century compilation transmitted them to medieval Europe, from which they were adopted by the civil law systems that govern most of the world outside the common law sphere today.