Yes, I am using Thucydides as one of my historians for the first section of the X-History exam. If you want to use him, what you need to do is find a some bit of info on his background (context), but most importantly, his history (The Peloponnesian War). Find out how, why and when he wrote his history (in other words, the historiagraphy). Add in a few quotes, and you're set for Thucydides. I apologise for not explaining this well, but I can't really put my method of investigating historians in words. Hope this helps, anyway.