Bill Marsh and other artists at The New York Times created this timeline of world atrocities over the centuries.  

Estimating the tolls from such horrors is an inexact science, given war’s nature and the mysteries of antiquity. The deadliest “multicides” are more plentiful in recent centuries, given that there were more people to kill and better ways to kill them on a grand scale. Even so, killings as a percentage of all humanity are probably declining. Here is a look at the sweep of human brutality presented in a timeline.

Click the image to see the full-sized version: