While sunglasses as such are a relatively recent invention, dating back to the earlier part of the 20th century, tinted lenses have been around for a lot longer. Pliny the Elder wrote that the Emperor Nero liked to watch gladiator matches through emeralds; in 12th century China, court judges used lenses of smoky quartz to hide their emotions from those they were questioning; In the mid 18th Century, James Ayscough began to experiment with blue and green-tinted lenses, believing that these could correct a number of sight conditions; and in the 19th and early 20th centuries, yellow and brown lenses were used in one of the many, pre-penicillin treatments of syphilis (based on the fact that sensitivity to light is one of the symptoms of the disease).

None of these had anything to do with protection from harmful ultraviolet rays. Indeed their popularity, once tinted glass became more widely available, came from their use by film stars in the 1920s. At that time it was commonly believed that sunglasses were worn by the famous to avoid recognition by fans. However, an alternative theory has been suggested more recently: Because of the low sensitivity of early film stock, dangerously high-powered arc lighting was needed on film sets. Prolonged exposure to these gave film stars very red eyes and sunglasses were worn to cover up a multitude of eye conditions. Whatever the reason, even once ultraviolet filters were developed for film-studio lighting, the popularity of wearing sunglasses continued among film stars, and of course the rest of us followed suit.

But how did the wearing of dark glasses by special agents, detectives, fearless but unorthodox crime-fighters etc. become such a cliché? I’m not saying all cops really do wear them (probably the reverse, though, then again, how do you know the man behind you wearing dark glasses isn’t tailing you?) but the image crops up often enough in the cinema and TV for it to have become a familiar association and one I’ve seen transferred to reality in some places, having had some interesting experiences involving Mexican law officers and the secret police of Tamil Nadu, several of whom had a predilection for these items of eyewear. There was also one other occasion:

I’d taken an overnight plane to Athens, arriving about 4am. My connecting boat didn’t leave till that evening so I had time to kill and decided to go and see the Acropolis at dawn. I missed the sunrise but it was still very early on a beautiful clear morning as I began my climb to the top of the hill. Hardly any people were about at that hour and the first one I passed was a man dressed in a dark suit and pale blue shirt open at the collar, standing next to one of the park benches. He was wearing sunglasses and carrying a folded newspaper. The suit surprised me, it seemed a bit formal for the setting, or that time in the morning. Then, a few yards later, I came across another man in a similar suit, light blue open-necked shirt, dark glasses and folded newspaper. Oddly enough, my initial thought when, a little further up the hill, I came across two more in similar clothes and accessories standing together silently, was that I’d stumbled into a gay cruising area. I decided that the suit, sunglasses and newspaper indicated some sort of code, but on seeing a fifth man lurking near some bushes a bit further on, again dressed similarly and with the same props, I began to revise my theory. What gave it away was the loud squawk that came from his newspaper, which, on second glance, seemed to have a short aerial sticking out of it. By the time I’d reach the Parthenon I had spotted about 15 more men, all similarly attired with folded newspapers, which, now I was looking for them, all had short aerials poking out from the top of them.

I have to say that, while I enjoyed the ancient architecture and statues, I was now more interested in finding out what was going on. However, it seemed a breach of etiquette to ask any of the men with folded newspapers, so I gave up and left.

Some time later as I neared the streets below, I heard the approach of a helicopter and, looking round, saw it begin to descend towards the Parthenon. This heightened my curiosity even more, but it was several days before I found out that my visit had coincided with that of Daniel Ortega then President of Nicaragua, who would have been arriving on the helicopter as I left.

At the time it made me laugh to think that I’d stumbled on possibly the most conspicuous plain-clothes operation in history, but it has since occurred to me that the reason why some film stars and certain members of security forces wear sunglasses is not to evoke anonymity, but the complete opposite: to say, I am here, I want you to see me, but don’t get any closer because I am important. If this is the case, then this particular use of sunglasses is not so different from their use by 12th century Chinese interrogators.