Just two examples:

1) The East:

If you walk from Simikot / Humla District, Western Nepal, upwards in the
valley of the Humla Karnali Goshi, you will, after a few days, cross the
Nara Lagna pass at 4580 m down into the valley. Near the hamlet Hilsa the
river forms the Nepalese/Tibetan boundary. Crossing the river - which is
easily possible on a bridge, absolutely devoid of controls - one climbs up a
promontory to reach the prominently looking Chinese "bordermarker", with the
characters for "zhong" and "guo" - Land of the Middle - facing Nepal (!),
something which is unusual for Western bordermarkers. Not only this, but
also the fact that the dark-grey concrete pillar is about 200 m off the
river bed indicates it is meant as a "warning" against all wild barbarians =
non-Chinese, to keep off and be impressed.

Walking on into Tibet, next came the village Sher - 3600 m - and a few miles
later the bigger village of Kojarnath. Here is the first Chinese police
station, with a timid young Chinese police officer holding out in his
hopeless position among hostile Tibetan locals. No controls either. Further
on, after another few miles, you will reach the little town of
Purong/Taklakot, where tea is waiting in the local guest house. Here you
will be met by Chinese green-uniform officials who will check your
passports, and, most important, stamp them, will have an interested look
into the smaller bags - the larger rucksacks remain unchecked. Finally the
friendly officials will stand up, together with the entire party, for an
"international friendship" group snapshot outside of the office. Afterwards
you are free to do whatever you like in Tibet - provided you find something
to eat.

Sorry, the pictures that I have are in my photo album.

2) The Soviet style:

You best take the former inner-German border. It was "ploughed" and
"unbroken", to speak in Mr. Nasarbajew's terminology. Ploughed means there
was a broad, staggered security strip, with watchtowers and shooting ranges,
so that anybody trying to cross the border - an absolute crime in
communism - could easily be detected and "liquidated". Unbroken means it was
completely tight, no holes in between. The border fortification line did not
follow the "official" delineation - there have been deviations of up to
several hundred metres. I remember a place in Bavaria, where, next to the
sidewalk of a West German road, there stood the East German border marker in
a deep forest, while the "real" border was far away "ploughing" through a
better controllable back-country area. These were places where you could
take foreign visitors to when they wanted to be thrilled by stepping into
East Germany un-punished.

In other words: The boundary fortifications served as a monument of warning.

Wolfgang