They are backed up by watchtowers fitted with infra-red radars and optical sensors purchased under SBInet before it was cancelled.

BBC: US-Mexico border: Efforts to build a virtual wall

From the parapets of the Pew Center and other such watchtowers of serious discourse, the prospects for maintaining an informed electorate look bleak indeed.

NPR: Excerpt: 'Strange Bedfellows'

Using clever juxtaposition, Asisi illustrates how Berliners coped with their warped reality, going about their business in the shadow of barbed wire and guards patrolling from watchtowers.

BBC: Bringing the Berlin Wall back to life

Standing on a hillside overlooking it, I can see trees pushing their way up through the roofs, vines twined around the gates, the watchtowers empty and abandoned.

BBC: Art classes and square eyes at Guantanamo Bay

The rest of it - the five watchtowers, concrete perimeter wall, 57 concrete 'kiosks' (which stored the nuclear warheads) and other testing and maintenance buildings - have deteriorated and the 'scheduled monument' has now been put on the at-risk register by English Heritage.

BBC: The battle to save England's heritage

It is an unlikely spot for a bohemian cultural centre -- along the banks of the barbed wire-lined Han River and within sight of the armed checkpoint watchtowers -- but the galleries, cafes and bookstores exhibit work from some of the finest artists and architects from Korea and abroad.

BBC: Make art not war in South Korea