It seems like a lot of you think Roland was either thrown back in time or he was sent into another dimension, but in this dimension or time he has possession of the horn. If he was thrown back in time does he have the memories from his last round with the Tower? Is he in another dimension with the horn but on his journey for the first time(in his mind). If it is a continuation from the journey we are privy to, does that mean only a few beams hold the tower together or are the beams that broke still broken? In that case the Tower would be even closer to destruction. I think that he was sent back in time and he is in another dimension, that being said there are as many beams holding up the tower as there were when WE(readers) met Roland for the first time. As has been mentioned before he has another piece to the puzzle in the form of the horn but not necessarily all the right pieces. As stated before Ka is a wheel and Roland has turned to the right place. The fact that Gilead fell hundreds of years ago just goes the fact that time is becoming thin. As Roland continued his quest years and years have gone by. After his conversation with Marten on the beach, Roland awakes thousands of years later. Time is thin.