the Wall itself seemed endless, and there were many aerial flybys coordinated with the music, and marching bands that paraded across the very long stage ... as I recall the Scorpions entered in what appeared to be a big Gestapo car
the geographic context was that the show was held in the historically loaded locale of Potsdamer Platz, a site which must hold as many ghosts as Pompeii but much more recent
theres a huge
Wikipedia article on Potsdamer Platz, which I only just skimmed, but I recommend for those interested in such thangs ... among other details Hitlers bunker was rumoured to be under the spot
the stage was along a bend in the Wall, immediately to the south of the Brandenburg Tor and a few blocks to the west of Checkpoint Charlie
Rogers Wall was literally on top of the ruins of the Soviets wall, and the audience was on the Western side looking towards the communist side ... hundreds of people were visible on the East Berlin rooftops watching the concert from behind
and I recall the gates were knocked down before the show was over, so 10s of 1000s more could force themselves closer (marginally) to the stage
someone on FlickR helpfully uploaded these graphics (thanks to the uploaders):

you see Potsdamer Platz labelled close to the topleft?
so Im thinking Rogers stage may actually have been closer to whats labelled the inner wall, and that big empty area would have been where the audience was?
hell I cant figure it out, but the airphotos apparantly from 1989, so aside from the real Wall being mostly dismantled the buildings should be mostly the same a year later
the Berlin government was just debating what to do with the lands near the Wall when Roger held his concert, and there were zany looking squatter camps right next to Checkpoint Charlie
and if Im following their conversation correctly, this is what the future site of Rogers concert looked like in 1975

and this is what it looks like now
