Various events over the past few days connected to St Francesca of Rome (1384-1440) have set me thinking about the enduring appeal of patron saints.

On Sunday I attended the blessing of cars, buses, taxis, police vehicles, fire engines and road rescue trucks (topped by giant cranes) outside the church of Santa Francesca (or St Frances of Rome) in the Via dei Fori Imperiali, by the Colosseum.

There was music from the Rome municipal police band and a mass conducted by Cardinal Angelo Sodano, the former Secretary of State, now the Dean of the College of Cardinals, whose titular church this is. At the end the drivers all sounded their horns, klaxons and sirens - quite a noise.

The following day, Monday, cacophony gave way to tranquillity: the Oblate order founded by St Francesca opened the doors of its convent, the Tor di Specchi, beneath Capitol Hill, the site of the Rome city hall (Campidoglio), the church of Santa Maria in Aracoeli and the Capitoline Museums. Pope Benedict XVI, who had been visiting the Campidoglio, was the first through the doors of the convent, for a private tour, followed later by the public.

This (and the next two Sundays) is the only occasion in the year when visitors can enter to admire the calm beauty of the convent and its extraordinary frescoes depicting the saint's life (including her temptation by devils and monsters with tongues of flame).

She is dear to the heart of Romans, and still revered for her good works for the poor in Trastevere, the once working-class artisan district across the Tiber (now much gentrified), where she handed out grain and wine during the 1402 famine. No less remarkable is the fact that Francesca Buzzi - or Francesca de Ponziani, to use her married name - founded an order even though she was married, with children.

It was only after she was widowed that she entered the order herself, and only on the insistence of her father confessor, a certain Don Giovanni (!), that she agreed to become Mother Superior (or so I learn from Lady Georgiana Fullerton's "Life of Santa Francesca Romana", quoted in the incomparable Augustus Hare's "Walks in Rome" - published in the 1890s and still one of the best guides to Rome).

Francesca is credited with many miracles in her lifetime - including healing a deaf and dumb girl by touching her tongue - and was canonised in 1608. Quite why Pius XI named her the patron saint of motorists is not clear: the Oxford Dictionary of Saints suggests it is because she had a "continuous vision of her guardian angel". One explanation is that when she went out at night on her missions of mercy the guardian angel went before her lighting the road with a lantern - rather like headlights.

She shares the patronage of motorists - and all travellers - with St Christopher, a third century saint from Asia Minor about whom much less is known, and who may not even have existed. According to legend, Christopher helped to carry travellers across the river near his home, and one day bore across the river a child so heavy he could hardly take the weight. He discovered that the child was Jesus, and that he had carried "the weight of the whole world and him that created and made the world" on his shoulders.

One of my other favourite patron saints is Saint Barbara, who keeps watch over artillery gunners, masons, miners, military engineers, stonecutters, and indeed anyone threatened by lightning or sudden and violent death. Since her origins, like St Christopher's, are possibly legendary, she was removed from the official Catholic calendar in 1969.

However, she continues to be popular: the story goes that she too was a third century Asia Minor Christian, the daughter of a wealthy pagan who was fatally struck by lightning when he beheaded her for her beliefs. Then there is St Joseph of Copertino, the seventeenth century Franciscan from southern Italy, who could fly through the air (he was known as "The Flying Friar") and is, inevitably, the patron saint of airmen - and of students taking exams, since although he could barely read or write, he was admitted into the friary because he happened to be asked the one question he had prepared for.

So it seems we still need patron saints, even if their feats, or indeed their origins, are the stuff of popular legend. New ones are still being proclaimed for modern times: the patron saint of the Internet is St Isidore, Bishop of Seville, (600-636), on the grounds that his "Etymologies", published in 20 books after his death, was an encyclopedia of all human knowledge of the time. The patron saint of journalists and writers is St Francis de Sales, the sixteenth century Bishop of Geneva, who was himself a writer, while those working in television enjoy the protection of St Clare of Assisi - because one Christmas, when she was too ill to leave her bed, she is said to have seen and heard Christmas Mass even though it was taking place miles away.