Analyzing historical information can show how a software system evolved into its current state, which parts of the system are stable and which have changed more. However, historical analysis implies processing a vast amount of information making the interpretation of the results difficult. To address this issue, we introduce the notion of the history of source code artifacts as a first class entity and define measurements which summarize the evolution of such entities. We use these measurements to define rules by which to detect different characteristics of the evolution of class hierarchies. Furthermore, we discuss the results we obtained by visualizing them using a polymetric view¹. We apply our approach on two large open source case studies and classify their class hierarchies based on their history.