Keep track of historical Pipeline Changes??

So I know views and dashboards report in real time in CRM....  But what if I wanted to see a comparison of something based on points in time?

For example say I wanted to see what my pipeline of opportunities was in December 2014 versus now in December 2015?

I've heard there might be a way to do this by creating an activity record every time a status changes on an opportunity but I can't figure out how to create a report or view that would show this...? 

Any advice on this?