When the new pope emerges into the spotlight, the eyes of the world will be on him.
The Gammarelli family have been papal tailors for generations
Everyone will be focused on his face, trying to get an impression of the personality of the man chosen to lead the Catholic Church.
But the Gammarelli family will be looking more closely at his white robes, checking to see how well they fit.
As papal tailors for generations, it is their job to make sure the newly elected pope has an outfit to wear.
Hanging up close to the Sistine Chapel will be white vestments in three sizes, ready to fit a pope who is small, medium or large.
"We received the order from the Vatican after the death of John Paul II," says Lorenzo Gammarelli.
"Four tailors have been working on it full-time, all week. We have made vestments of wool and silk in each size, so there are six sets in all."
The firm is famously discreet about its distinguished customers.
But family pride was indulged by displaying the finished papal garments in the window, before they were sent to the Vatican.
Not, of course, that there was anything to identify the vestments, apart from the fact they were white.
The new pope will almost certainly be one of the 115 cardinals who enter the conclave on 18 April.
There will be only a short time between the white smoke that announces his election and his first appearance on the balcony of St Peter's Basilica.
Cardinals come in all shapes and sizes, and some are generously proportioned. So will the off-the-peg robes cover all eventualities?
"We seldom make a mistake, so there is a good chance they will fit," Lorenzo says with a smile.
Last minute fitting
Behind the scenes at the Vatican, nuns will be ready with needles and thread to make any last-minute adjustments.
After the pope's election, the firm will be hoping for a phone call to arrange a proper fitting.
Lorenzo Gammarelli outside the papal tailors
After his election, a new pope has to acquire a whole new wardrobe. It really is a case of "I've got nothing to wear".
The new man will be free to choose his own tailor, but most recent popes have been happy to use the Gammarelli.
The business was founded in 1792, and Lorenzo is the sixth generation of his family to join the firm.
The premises are in a side street close to the Pantheon, but most tourists pass by without recognising the shop.
Stepping inside is like entering a very traditional firm of gentlemen's outfitters.
The shop fittings are all polished wood, and the shelves are stacked with rolls of cloth in every ecclesiastical colour - black, purple, red and white.
Many senior clerics have been coming here for years, in some cases since their student days in Rome.
Being tailors to the pope must help business, but the staff like to think it is the quality of the material and the cut of the cloth that keeps their customers coming back.
"We are proud of our work," says Lorenzo Gammarelli.
"We are famous for the quality of our clothes. People do not come here just because of the pope. They come here because we make good cassocks."
The framed portraits of former pontiffs hanging on the walls are the only indication of the firm's distinguished clientele.
The white robes worn by John Paul II on his trips around the world must have been seen by more people than any other set of clothes.
The tailors at Gammarelli say they never think about it; their only concern is making sure the pope looks his best.
"For the family, it is an enormous honour to make clothes for the pope," Lorenzo says simply.
It is a tradition the firm hopes will continue after the election of the new pope.