“What does ultima ratio regum mean?”

’The Last Argument of Kings,’ the Librarian says.
’King Louis XIV had it stamped onto the barrels of all the cannons that were forged during his reign.’

– Snow Crash by Neal Stephenson

The photo is from Reivax’s Vienna 2003 photoset, and is the best of photos I could find with the quotation on.  You may see more of his photographs here.