The first book, Justine, tells about the narrator's life in Alexandria, including his girlfriend Melissa, and the affair he has carrying on with Justine, the wife of a friend of his.
In the second book, Balthazar, the narrator finds out that Justine was not in love with him at all, he was the "beard," so that her jealous husband wouldn't find out about her real lover. This causes him to go back and re-examine everything he described in the first book in the light of that new information.
The third book, Mountolive, is in the third person, involving many of the same characters, including Justine's husband and his family, and the narrator of the first two books barely appears. It takes place during the same timeframe as the first two.
The final book, Clea, moves forward in time and shows what happened to some of the characters after the other books (though the fate of some of the characters is left ambiguous).
I never made a conscious decision to use this technique, showing something and then showing it again with more information (backing the camera away from the action, as I think of it), but I'm sure this is where I got the idea. I was reading quite a bit of Durrell when I started writing what turned into U-town (and several of the cut-ups at the beginning of the new novel, which were originally in the beginning of U-town, were of The Alexandria Quartet).
To dump a reader right into everything going on before and during the Kingdom Come gig at the Quarter would just be confusing and annoying. So, I show it first more or less from the point of view of Chet (who is outside most of the events), then later I show it from Pete's viewpoint, including the events of that afternoon and the aftermath of the gig itself, then after that I show that there was a major person in Pete's life at that time who didn't happen to be at the gig itself, and then later still I show the earlier part of that day.
And throughout the whole book, of course, I show what happened after that night.
And then, as with Clea, the narrative in the final part of the novel straightens out and moves forward (well, sort of "forward" 🙂 ).