You can find placemarks in high res of 130 ancient theatres (roman and greek) all around the mediterranean sea. At least 150 more are in low res area.
Caution : there are only Theatres (half-circular form) here and not
Amphitheatres (full elliptical form).
For amphitheatres, you can see the post :
http://bbs.keyhole.com/ubb/showthreaded.php/Cat/0/Number/143706/an/0/page/0#143706

special thanks to :
http://perso.wanadoo.fr/claude.philip/Pays/italie/frame.htm
http://italia.novaroma.org/signaromanorum/
and Korovieff, and Pompilos .