One of the hardest parts of learning music history (and I suppose art and other histories as well) is that though styles change over time, the changes happen extremely scattered with little uniformity. Thus students tend to believe that a more "advanced" sounding piece was composed later than a "simpler" sounding one, when the opposite is also extremely likely to be true. One of the biggest recurring problems for learning style in Early Music, for instance, is that the most commonly studied pieces in English Renaissance style are being composed at the same time or after the Italians created new techniques of recitative, basso continuo, and other markers of the Baroque.
This Timeline + Map, developed by myself and Natasha Skowronski (MIT '10) allows viewers to see what pieces were being composed at the same time or in close geographical spans of each other. Each piece (taken from a mix of my syllabus and Craig Wright's Music in Western Civilization) has a thirty second excerpt online while a few have associated YouTube videos. (Students in the class can hear whole pieces). Click the image below to investigate further.