[SunkenCiv]

Yes, of course it is. The amphitheater is diagnostic of classic Greek architecture, and to some extent the Roman-era borrowing of it.

[SunkenCiv]

Theater:

http://www.travbuddy.com/photos/blogs/2691073

http://www.travbuddy.com/photos/blogs/2691075

Note the use of the arch, this is classical, not Mycenaean:

http://www.travbuddy.com/photos/blogs/2691071

http://www.travbuddy.com/photos/blogs/2691074

[WhiskeyX]

Natural amphitheaters were in existence in the natural rock formations before Humans existed, and the stone age human cultures found such natural amphitheaters to be natural meeting places worthy of artificial emulations. So, what makes you think this particular amphitheater can only be an origin in What Dlassical Greek Timeline; i.e. when?