There ought to be a certain point in one’s training for the post of transitionary (our official job title – clunky, I know; I prefer the sobriquet “flitter” – or “transitioner” or “transitioneer,” at a pinch) when one realises that one has discovered or acquired an extra sense. It is in a sense the sense of history, of connection, of how long a place has been lived in, a feeling for the heritage of human events attached to a particular piece of landscape or set of streets and stones. We call it fragre.

Part of it is akin to having a sharp nose for the scent of ancient blood. Places of great antiquity, where much has happened over not just centuries but millennia, are often steeped in it. Almost any site of massacre or battle will have a whiff, even thousands of years later. I find it at its most pungent when I stand within the Colosseum, in Rome. However, much of it is simply the layered result of multifarious generations of people having lived there; lived and died, certainly, but then as most people live for decades and die just the once, it is the living part that has the greatest influence over the aroma, the feel of a place.

Certainly the entirety of the Americas has a significantly different fragre compared to Europe and Asia; less fusty, or less rich, according to your prejudices.

I’m told that New Zealand and Patagonia appraise as terribly fresh compared with almost everywhere else.

Myself, I love the fragre of Venezia. Not the fragrance – at least, not in summer, anyway – but very much the fragre.

I prefer to arrive in Venice by train, from Mestre. As I disembark at Santa Lucia station I can, if I declutch my senses and memory, fool myself into thinking that I have arrived at just another big Italian railway station, one more terminus amongst many. One walks between the towering trains, crosses the indifferent commercialism of the rather brutalist concourse and expects to find what one would find anywhere: a busy road or square, another bustling vista of car and truck and bus – a pedestrianised piazza and a few taxis, at best.

Instead, spreading beyond the sweep of steps and the scatter of people – the Grand Canal! Light green choppy water, the churning wakes of vaporetti, launches, water taxis and work boats, reflected light slicing off the waves to dance along the façades of palazzos and churches; spires, domes and inverted-cone chimneys ranged against a sky of cobalt shine. Or against milky clouds, their mirrored pastel tones softening the restless waters of the canal. Or against dark veils of rain cloud, the canal flattened and subdued under a downpour.

The first time I visited the place was for the carnival in February. I discovered mist and fog and quietness, and a chill in the air that seemed to rise from the water like a promise. My name was Mark Cavan. My languages were Mandarin, English, Hindustani, Spanish, Arabic, Russian and French. The Berlin Wall was already history, though still mostly standing.

It was your world.

Some way down the Grand Canal, on its west bank, sits an imposing near-cubical palazzo. Its walls are a glacial white, the shutters shielding its many windows matt black. This severely formal and symmetrical building is the Palazzo Chirezzia, once the home of a Levantine prince, later that of a cardinal of the Roman Catholic church, then for a hundred and fifty years an infamous brothel. It belonged, then as now, to Professore Loscelles, a gentleman who knew about and was sympathetic to the Concern. Back then, he simply made himself, his money and connections useful to us, and, equally, gained much through the association. He has since risen to join the ruling Central Council, though on that cold February morning twenty years ago this was still an ambition of his.

I had been invited to the city and the carnival as a reward for my services, which had lately been energetic if not onerous. There were no other transitionaries present, though there was a gaggle of Concern apparatchiks and officials, all of whom were polite to me. Despite the rather generous amount of blood I had on my hands even then, I was still not yet used to the idea that people who knew of my role within l’Expédience might find my presence intimidating, alarming or even frightening.

Professore Loscelles is a modest figure of a man, verging on short, though with a stately bearing which belies this. He is one of those who grow in isolation. Alone, one might swear he is as tall as oneself; in a small group he seems to shrink by comparison and in a crowd he disappears entirely. He was balding then, losing thin brown hair like seaweed dropping back from a rock with a receding tide. He has a splendid hook of a nose, prominent teeth and eyes of a frosty-looking blue. His wife was dramatically taller than him, a statuesque Calabrian blonde with a large, honest-looking face and a ready laugh. It was she, Giacinta, who taught me the dances which would be required at the series of balls to which we had been invited. Happily I am a quick learner and apparently I move well.

The palace contained a ballroom where one of the great masked balls of that year’s carnival was to be held. This took place the day after I arrived. I was appropriately entranced by the fabulous masks and costumes and by the sumptuous decor of the ballroom itself; a hymn of ancient, polished woods, glossy marble and extravagantly gilt-framed mirrors, all lit entirely with candles, imparting a distinct mellowness to the light and a smoky scent to the air, like incense. It mingled with the odour of perfumes and the smoke from cigarettes and cigars. The men were peacocks, the women whirling, dazzling belles in glittering gowns. A small orchestra in antique dress filled the space with melody. Three enormous chandeliers of red glass oversaw it all – great swirling, abstract shapes looking like vast surges of glistening blood caught in the act of spinning within an unseen whirlpool – but were reduced to mere pendulous sculptures reflecting candle flames, their bulbs unnecessary and unlit.

Breathless, gripping a glass of Tokaj, I stepped out onto a little terrace bounded by fat white marble balustrades shaped like tears. A small crowd of partygoers stood quietly watching snow descend against the lights of the few passing boats and the light-flecked buildings on the canal’s far side. The spiralling chaos of flakes appeared from the darkness overhead as though created by the lanterns of the palazzo and disappeared silently into the oily blackness of the gently moving waters before it.

I went out early the next morning into that cold, encasing whiteness, my breath spreading into the dark narrow spaces in front of me, and found some untrodden stretches on the Sestiere Dorsoduro. I strolled the ancient, hidden stones, breathing in the cool, clear salty scent of the place and soaking up the world’s fragre. It tasted, of course, of all the things that all the other worlds taste of, but the identifying highlights spoke of a kind of seductive cruelty, an orchidaceous venality, so infinitely sweet it could only be redolent of corruption and decay. Here, in the eternally sinking city, with that odour of glamourous savagery filtering through my mind like mist off the lagoon into a room, it all felt spent here but only paused elsewhere, like something waiting to resume.

The snow lay across the city for the next few days, creating a starkness beneath those sea-wide skies, draining colour from the passing clouds, water and buildings and promoting the views of that city of Canaletto and fractious colour to a ravishing monochrome.

The final ball was held in the Doge’s Palace in a vast and splendid room built half a millennium ago to house two thousand milling princes, merchants, ambassadors, captains and dignitaries. An airstream originating in Africa had pushed up over the heel of Italy and the Adriatic, melting the snow and bringing mists and fog as it collided with and was slowed by contesting winds spilling down from the mountains to the north. The city seemed to submerge beneath the resulting vapours, cloaking itself in veils and shrouds of moisture.