Spring, 1745. Carnival fever grips Venice. Music and confetti fill the air; masked figures move mysteriously in the shadows; jovial couples in lavish costumes cross piazzas en route to glittering balls. But one couple has a date with history.
Spellbound by a lady's beauty, the man who would one day become the world's most famous seducer springs into action. The fact that she was a noblewoman was inconsequential, that she was with her husband a mere inconvenience.
Posing as a state official, Giacomo Casanova frogmarched the hubby to San Giorgio Maggiore – a tiny island opposite St Mark's Square – before wining and dining his wife at Do Spade, a cosy tavern tucked away behind the Rialto market. Falling for Casanova's irrepressible charms, she soon became another notch on his worn bedpost.
At least he bought her dinner. Rather more romantic meals will doubtlessly be in evidence in Venice exactly one month from today, when the classic Valentine's Day break to the city will be in full swing, along with this year's Carnevale. But Casanova's legend lives on. Indeed, the barmaid at Do Spade took great delight in retelling the Casanova story as I stopped by for some meatballs and a glass of red: a refuelling stop Casanova often made.
Born to actors in 1725, Casanova railed against his lowly roots. "To be an actor in the 18th century was little better than being a prostitute," explained my guide, Rita Sartori, as we reached the spot where it all began. A plaque on Calle Malipiero, a typically narrow Venetian street of crumbling brickwork, marks Casanova's birthplace.
A sickly child, one of his earliest memories was apparently travelling by gondola to a witch doctor on the island of Murano. He was cured by what he described as a "magical ritual", which sparked a lifelong fascination in medicine, alchemy and black magic.
But first, the church beckoned. Casanova left Venice, aged nine, to be educated in Padua. He returned six years later as an apprentice priest. The future looked bright. His first sermon took place at the San Samuele church, which overlooks the Grand Canal. It was also the site of his baptism, his parents' wedding and impressive 15th-century frescos. Sadly it is now closed to the public.
The priestly Casanova was a success, with donations – and the odd love letter – flooding in. His second service, however, was described as being drunken and delirious, and signalled the first of many career changes. Violinist, librarian, theatre manager and secret spy are among the professions later to adorn his CV.
We strolled along Calle Larga XXII Marzo, a busy thoroughfare of luxury stores. At the far end stands the imposing church of San Moses. This house of God was once surrounded by houses of another kind: gambling dens that fed Casanova's other passion. His favourite spot for a game of cards is now the well-preserved marble breakfast room of the Hotel Monaco & Grand Canal near St Mark's.
Given his promiscuity (112 conquests by his own reckoning), it's hardly surprising Casanova picked up the odd nasty infection. He is said to have cured himself of 11 bouts of syphilis by administrating mercury; such forward-thinking won him city-wide admiration. But, others didn't take so kindly to his outspoken views on science and medicine.
The police came knocking at dawn on 26 July 1755. For the next 16 months, Casanova was kept at His Doge's Pleasure. A guided tour of the Doge's Palace reveals the reality of Casanova's incarceration – and his escape. I reached the rafters of the 14th-century Gothic residence through a secret staircase beyond which the wood is no longer gilded and the walls are devoid of art work.
You have to crouch to enter Casanova's cell high in "the leads" directly beneath the slated roof. The room is nothing more than a bare floor with a single barred window; I sympathised with Casanova, who stood over 6ft tall. No wonder he requested an armchair.
Fearing a lifetime here, he plotted his escape. In what is probably his finest hour (fathering his own grandson being his lowest), he began carving through the floorboards under his armchair. But he was foiled just hours before his bid for freedom, when he was transferred. He tried again, this time helped by Balbi, a monk. They fled in the dead of night but found themselves locked in the Doge's grand Square Atrium.
Undeterred, Casanova opened a window and called out to a watchman, who, thinking they were respectable guests, rushed up to let them out. The escapees left via the Golden Staircase, Alessandro Vittoria's white stucco and 24-carat gold masterpiece.
Of course, Casanova did not flee into the night never to be seen again. Instead, he crossed St Mark's for a coffee amid the frescos and hand-painted mirrors of Caffè Florian. I popped in to ponder his escape – but at €9 for a cappuccino I quickly thought better of it.
Before leaving, Casanova took one last look at his homeland. He would not return for nearly 20 years. He describes the moment in his autobiography: "I... looked at the entire length of the beautiful canal and, seeing not a boat, admired the most beautiful day one could hope for."
Travel essentials: Venice
* The writer travelled with Cox & Kings (020-7873 5000; coxandkings.co.uk), which offers three nights' B&B at the Ca' Sagredo hotel, with return flights from Gatwick from £395.
* Airlines serving Venice include BA (0844 493 0787; ba.com) from Gatwick and Heathrow; easyJet (0843 104 5000; easyjet.com) from Gatwick; and Monarch (0871 940 5040; monarch.co.uk) from Gatwick, Birmingham and Manchester.
* Doge's Palace Secret Itinerary tours (museiciviciveneziani.it) cost €18.
* Do Spade (00 39 41 521 0574; cantinadospade.it). * Caffè Florian (00 39 41 520 5641; caffeflorian.com)
* italiantouristboard.co.uk n The History of My Life by Giacomo Casanova