Is there are real diamond or cross placed all over rome?

Once again, not everything his his books is fictitious. Maybe you've never read a Dan Brown book, but perhaps you should before you start reviewing them.

I have read the book. Authors have a way of exaggerating things for creativity thus making them fictitious. This is the main reason why he got in trouble with his Da Vinci Code, he put there 'some are from actual places and events' this should not be because he's neither a historian or an expert on the subject matter. These books are there for fun-reading brought about by a person's imagination. Yes, indeed landmarks are true to set up the reader's mind as to how the location looks like (for it happened in Rome, Vatican in that story), just like the stories of Sherlock Holmes is as they point out the 'look' of London. Authors are allowed to do this in order for people to 'relate' as to how the venues look like plus allow the readers to feel the processes. They can intertwine reality from fiction but still it's considered fiction. You can well search wikipedia or any dictionary or reference you may find for fiction so as to understand it fully. Good luck.