Analyzing historical information can show how a software system evolved into its current state, but it can also show which parts of the system are more evolution prone. Yet, historical analysis implies processing a vast amount of information which makes the interpretation difficult. To address this issue, we introduce the notion of history of source code artifacts as a first class entity and define measurements which summarize the evolution of such entities. We then use these measurements to define polymetric views for visualizing the effect of time on class hierarchies. We show the application of our approach on one large open source case study and reveal how we can classify the class hierarchies based on their history.