Christopher Nolan than went on to explain that Batman Begins, The Dark Knight, and The Dark Knight Rises are all based off of different genres of film that are defined by the villain in each particular movie.
You can read more of what Christopher Nolan had to say about his Dark Knight trilogy over at Variety.
The origin story and crime drama of Christopher Nolan’s Dark Knight trilogy are easy to spot, but the historical epic might need some more digging.
Lastly, in 2012’s finale, The Dark Knight Rises, Nolan sees, “this historical epic.