In his inaugural lecture as Regius Professor of Civil Law at Cambridge, David Johnston argues powerfully that modern legal systems have much to learn from legal history, and from the methods and approaches of their predecessors. Roman law in particular equips them with the necessary rigour to allow them to develop coherently, and successfully to face new challenges. Professor Johnston argues that as legal history repeats itself, it is able to supply a fund of rules and principles ready for exploitation. These rules are not constrained simply because they were shaped and formulated in remote societies and different contexts, but should be seen as a valuable resource for modern legal systems.