Christopher Nolan says goodbye to his Batman trilogy in the foreword to the book The Art and Making of The Dark Knight Trilogy:
People ask if we’d always planned a trilogy. This is like being asked whether you had planned on growing up, getting married, having kids. The answer is complicated. When David and I first started cracking open Bruce’s story, we flirted with what might come after, then backed away, not wanting to look too deep into the future. I didn’t want to know everything that Bruce couldn’t; I wanted to live it with him. I told David and Jonah to put everything they knew into each film as we made it. The entire cast and crew put all they had into the first film. Nothing held back. Nothing saved for next time. They built an entire city. Then Christian and Michael and Gary and Morgan and Liam and Cillian started living in it. Christian bit off a big chunk of Bruce Wayne’s life and made it utterly compelling. He took us into a pop icon’s mind and never let us notice for an instant the fanciful nature of Bruce’s methods.
Read the rest at Vanity Fair.