<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>
<http://pop.h-cdn.co/assets/cm/15/05/640x320/54caf1e351383_-_onager-catapult-0812-de.jpg>
<http://www.popularmechanics.com/home/how-to-plans/how-to/a7921/early-adopter-build-this-onager-catapult-11556480/>