Is that Checkpoint Charlie? Incidentally, I see there's a mini version
of the old US border post still there, with actors posing as US guards,
who'll pose in pics with tourists for a fee. But there's no sign of the
old Soviet checkpoint.


Yes he means Checkpoint Charlie. The DDR referred to their border crossing
as Ubergangstelle Friedrichstrasse Zimmerstrasse and it was only available
to the military, diplomats and none Germans. Germans had to use
Heerstrasse, north of the Reichstag, though there were latterly other points
for West Berlin residents


AFAIK the checkpoint cabin erected and staffed by the Americans at that
point didn't check civilians coming through. There were no West German
authorities there.

As far as military patrols were concerned uniformed patrols were carried out
by the four powers in all sectors of Berlin. I got talking to a British
soldirer from Nelson in Alexamderplatz - the Russions patrolled and also
manned their victory memorial on 17th June strasse (West of the Brandenberg
Gate). And also Spandau Jail when it was their turn.

As Friedrichstrasse also acted as an interchange between two West Berlin S
Bahn lines and one West Berlin U Bahn line (U6) it would have been
impossible you would have needed 5 border controls (2 on the North Sud
Bahn, 2 on U6 and 1 on the Statdbahn at Lehrter Statdbahot to check
everyone).