So, I had to go to Pompeii to stand in that amphitheatre. What I found was that (with reference to the interview extra feature on the Director's Cut DVD...er, do I sound like a Pink Floyd geek?) Adrian Maben was 1) inspired to have staged the filming there (1971), 2) quite right about the eerie silence within the amphitheatre, 3) ridiculously diligent in setting up cameras in multiple, multiple locations around the ruins of the town (which are far more extensive than you'd guess) to get all those filler shots when you aren't watching the boys play live, as well as in trekking up the hill to get those fantastic shots across the Gulf of Naples.
Anyway, I haven't uploaded more shots of the amphitheatre yet, but here's what it looked like from ground level in December 2010. If you watch the DVD, on the oval stage there is quite a lot of high grass that's grown nearest the inner walls, which is now gone. The grass is now short, green and very lush. The pine trees behind the amphitheatre (not shown here) have not grown all that much in 40 years...
OK, done with the nerdiness now.