User blog comment:San&Ashitaka/TITAN THEORIES/@comment-27441457-20160628000501

I've got a big hunch that the Titans were some sort of biological superweapons created by technology that far exceeds our modern tech. The origin of their creation might have some connection to the calendar used in AOT. Maybe the Titans were first created 850 years before the story, but they didn't appear on a global scale until 743 years later.