In 1786, Jeremy Bentham (the philosopher and social theorist who made great inroads in the fields of ethics, jurisprudence and political philosophy, as well as being the "spiritual", if not actual, founder of UCL) visited his brother Samuel in Russia, who was working for Prince Grigory Potemkin helping administer the new provinces the country had won in the Russo-Turkish War. There, Samuel suggested to him the idea of a circular building at the core of a larger compound, by which a few guards could oversee a much bigger group of workers.
Jeremy took the idea and ran with it, eventually publishing his plans five years later under the title Panopticon; or, The Inspection-House . He laid out his idea for a great building, focusing specifically on the application of his ideas to a prison, but emphasising the flexibility with which they could apply to hospitals, schools or "mad-houses". As his brother suggested, it would be circular building, with a glass lantern in the middle where the guards would keep watch, "roughly the size of Ranaleigh [sic]", meaning the rotunda at Ranelagh Gardens in Chelsea:
The Ranelagh Rotunda, as painted by Canaletto. The picture now hangs in the National Gallery
But Jeremy improved his brother's idea in one crucial way. As well as allowing just a few guards to administer an entire prison, his plan involved concealing the inspectors from the view of the prisoners, "by blinds and other contrivances". The idea then is that the prisoners are forced to act as though they're being watched, even if there's no one in the watchtower at all.
In practice, this element of the idea was too cumbersome to pull off. It was one thing, with 18th and 19th century technology, to obscure where someone was looking; but it was quite another to obscure whether they were even present at all, in a building which must, to be effective, allow occupants to look out from 360 degrees.
Philosophy students, on learning about Bentham and the panopticon, tend to assume it was a thought experiment, designed to elaborate some aspect of the human psyche. It wasn't; he actually spent the better over a decade trying to get it built, before billing the government £700,000 (just under £50m in 2012 pounds) for his time. They paid him £23,000.
But the fact that Bentham's panopticon was never built doesn't mean it never existed. In fact, prisons around the world incorporated his ideas, although few of them attempted to implement the hidden-observance aspect of it, even after inventions like two-way mirrors would have made it practical to do so. The two best-known (and photographed) ones are in the Americas.
Image from a period postcard.
The Stateville Correctional Center in Illinois (above) has the circular building, central guard tower and stacked cells, and the Encyclopaedia of Chicago  confirms the Benthamite influence. The prison itself is still open, and the roundhouse block is now used to segregate inmates from the general population, as well as holding prisoners awaiting trial or transfer.
Photograph: Wikimedia Commons
The Presidio Modelo, a Cuban "model prison" built on an island off the country's south coast in the 1920s, was also built to a panopticon design. Tourists can now visit the prisons , which have four panopticon blocks, and a fifth where speaking was banned.
Photograph: Wikimedia Commons
It's not hard to see why the panopticon idea has fallen out of fashion. For one thing, it was a surprisingly inefficient way of holding prisoners; the large central area required means that the jails based on the idea take up a lot of room compared to more traditional designs. And the real problems with prison discipline have never been prisoners in their cells, but in communal areas – which a panopticon design can't really help with.
But the biggest reason is obsolescence. Where technology initially prevented actual prisons from employing the continuous observance aspect, it's now standard thanks to CCTV. And not just in jails, either. For most of us in our daily lives, we're never quite sure whether anyone else is watching. Even if we aren't moving, our electronic communications could be being observed. Bentham's vision arrived, two hundred years late. And he's still owed £677,000 for his time.