Excited by what I had seen, I began to look into the history of night climbing more deeply. In 1898, The Roof Climber’s Guide to Trinity was published. This was the first manual which attempted to document the physical environment of the Cambridge rooftops. It was also intended as a satire on the pompous tone of the Alpine climbing manuals available to the Victorian climber. This was followed by Whipplesnaith’s The Night Climbers of Cambridge in 1937, and Hederatus’s Cambridge Night Climbing in 1970. All these books contained stories of each ascent, together with technical information on the routes and photographs of the climbers taken in the dead of night, or as dawn broke over the city. As the subjects of the photographs and the photographers would be on adjacent buildings, some of the pictures show extraordinary action scenes, such as a climber stranded on the bare face of a wall as policemen wait for him at the bottom, or captured in motion flying through the air between two vertiginous ledges.

College authorities used the earlier guides to help them defeat the climbers. Concerned for the safety of their young charges they sealed the routes up their buildings, installing spikes, moving lightning conductors and cementing hand holds. As a result the latest instalment, Cambridge Nightclimbing, is deliberately reticent when it comes to some of the more precise details – if there is only one way up a building, they will relate how to get to the bottom of it, and leave the rest up to imagination and ingenuity.

I made only one attempt at night climbing myself, but I couldn’t get further than a chimney pot about three feet from my point of embarkation. Most people say that fear recedes into the background the second you actually start on the climb. In my experience it intensifies. It took me half an hour to get both legs out of my friend’s bedroom window on Neville’s Court, and once it took another two hours to coax me back in by mobile phone.

Modern life is encroaching on the delicate ecosystem of the midnight climber. The Fitzwilliam Museum, which was long recommended as a good novice climb, was lost to would-be adventurers in a recent renovation, which covered the building with alarm systems. Clubs and pubs in the city stay open later, which means that the silent and empty hours in which nightclimbing thrives have been cut back. The first inspiration of young climbers, the need to get into their colleges at night after the doors had been locked, has also been removed; the curfews that until the mid 1970s ruled the lives of all undergraduates are a thing of the past in Cambridge.

Nevertheless, the night climbers are still going strong. They have always been an anonymous bunch (all their stories are written under pseudonyms, and discovery means being expelled from the University), but they love to tell stories. In a recent investigation by The Times, one ex-climber told that, when he went up to the roofs on a particularly fine night, he met two other parties of men on a similar expedition, and they wound up having a spontaneous party in the air above the streets. So if you visit Cambridge, and find yourself wandering through the streets in the evening, it might be worth having a look at the sky. If you’re lucky, you might see one of the gargoyles move . . .