What is that thing?
The symbol for Christians in battle. The shields in the movie 300 had them.
https://www.google.com/search?q=spartans+shield&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=_EsJUemyJcKligKi3oGoBg&biw=864&bih=602&sei=AEwJUdqnCumsiALOwYCABQ