Bologna by the Numbers: a journey through maths, science and surprising facts
Updated on 05 March 2020 From Bologna Welcome
Like the chapters of a mathematics book, the buildings of Bologna’s historic centre bring geometry to life, conceal calculations and tell the stories of remarkable people. There is the Bologna of towers, porticoes and piazzas. And then there is another Bologna, waiting to be discovered, made up of numbers, measurements, geometry, scientific experiments and optical illusions.
All it takes is a change of perspective to discover that a basilica can become an astronomical instrument, a tower can help prove that the Earth rotates, and even a tagliatella can have a width calculated in relation to one of the city’s most iconic landmarks.
From the historic centre to the hills, here is an unusual itinerary through mathematics, physics, astronomy and fascinating curiosities. Ready to do the maths?
In Bologna, the numbers add up. And sometimes, they surprise you!
San Petronio: when the Sun enters the church
The first stop is in Piazza Maggiore, inside the Basilica of San Petronio.
Here, in 1655, astronomer Giovanni Domenico Cassini created a meridian line about 67 metres long, considered the longest in the world.
But how does it work? Through a small hole high up in the basilica, sunlight enters the building and projects an image of the Sun onto the floor. When the image crosses the meridian line, it marks local solar noon.
An ingenious system that made it possible to observe and study the apparent movement of the Sun throughout the year.
Palazzo d’Accursio: how long was a Bolognese foot?
We stay in Piazza Maggiore, but this time turn our attention to Palazzo d’Accursio.
On its base is a marble plaque preserving some of the traditional units of measurement once used in Bologna, before the introduction of the metric system. These include:
the Bolognese foot, measuring around 38 centimetres;
the pertica, equivalent to 10 feet;
the braccio, measuring around 64 centimetres, together with the double braccio.
Alongside these linear measurements are also models showing the standard dimensions of a brick and a roof tile.
A kind of public ruler from the past, particularly useful in a square that was, for centuries, at the heart of the city’s commercial life.
The Voltone del Podestà: have you ever tried whispering across a vault?
Beneath the Voltone del Podestà, just a few steps from Piazza Maggiore, stand in two diagonally opposite corners and speak while facing the wall to experience a surprising acoustic effect.
The result? Even whispered words can be heard clearly on the opposite side of the vault, several metres away.
The secret lies in the particular shape of the structure, which allows sound waves to travel from one corner to another.
It is one of Bologna’s most curious acoustic phenomena and, above all, a small physics experiment you can try for yourself.
Santo Stefano: why is it known as the Seven Churches?
Let’s move on to Piazza Santo Stefano, home to one of Bologna’s most fascinating religious sites, commonly known as the Seven Churches complex.
The name has a clear symbolic and sacred meaning rooted in the mystical numerology of the Early Middle Ages, rather than simply referring to the number of churches, which today is no longer seven.
The complex is in fact the result of centuries of transformation, during which churches, courtyards and other sacred spaces were built, modified and connected to one another.
The number seven is therefore not just a matter of quantity: in medieval Christian tradition, it also carried a strong symbolic and spiritual meaning.
This symbolism can be traced through the spaces, architectural elements and geometric decorative motifs of the complex.
Here, mathematics meets history and religious symbolism, reminding us that in the Middle Ages numbers could express far more than quantity alone.
Palazzo Poggi and the Specola: eyes on the sky
In Via Zamboni, Palazzo Poggi tells the story of one of the most important periods in Bologna’s scientific history.
The collections of the former Institute of Sciences preserve objects and evidence relating to physics, natural history, anatomy, nautical science and the study of natural phenomena.
But for those fascinated by numbers and stars, the real highlight is the Specola Tower, Bologna’s historic astronomical observatory.
For more than two centuries, scholars observed the sky here using instruments such as telescopes, astronomical clocks and other measuring devices, seeking to understand the movements of celestial bodies and the phenomena of the heavens.
Today, the Museo della Specola preserves numerous scientific instruments that reveal how methods for observing and measuring the sky have changed over time.
It was in this very tower that Bolognese physicist and mathematician Giovanni Battista Guglielmini began his experiments on falling bodies in 1790, seeking evidence of the Earth’s rotation, before continuing his research at the Asinelli Tower.
Asinelli Tower: how can you prove that the Earth rotates?
Not far away, the Asinelli Tower became the setting, between 1790 and 1791, for a famous scientific experiment carried out by physicist Giovanni Battista Guglielmini.
The idea was simple, at least in theory: drop several lead spheres, each one inch in diameter, from the Asinelli Tower, which stands around 97 metres high, and measure precisely where they landed.
The result? The spheres did not fall exactly along the vertical line, but showed an eastward displacement of around 17 millimetres.
The experiments, begun at the Specola Tower and continued at the Asinelli Tower, helped provide one of the first direct experimental demonstrations of the Earth’s rotation, more than fifty years before Foucault’s famous pendulum.
Please note: the Asinelli Tower is currently closed to the public due to works taking place in the Two Towers area.
Bolognese tagliatelle? It’s all a matter of millimetres!
In Bologna, the leap from physics to food is shorter than you might imagine.
In nearby Palazzo della Mercanzia, home to the Chamber of Commerce, a golden sample of the authentic Bolognese tagliatella is preserved. Its official dimensions were registered in 1972 by the Italian Academy of Cuisine.
Its established width is 8 millimetres after cooking, equal to 1/12,270 of the height of the Asinelli Tower.
A proportion that brings together two apparently distant symbols of the city: a medieval tower and one of the most famous pasta shapes in Bolognese cuisine.
Palazzo Pepoli: history is a matter of numbers too
How do we measure time? And how do we study a natural phenomenon such as an earthquake?
At Palazzo Pepoli – Museum of the History of Bologna, numbers become a tool for telling the story of the city and the development of scientific knowledge.
The museum route takes visitors through centuries of Bolognese history, using objects, reconstructions and multimedia installations to show how Bologna has changed over time.
Scientific themes include the measurement of time and the study of natural phenomena, including earthquakes: opportunities to discover how observation, measurement and calculation have helped us understand the world around us.
Here, mathematics is not simply a formula written on a sheet of paper. It is also a way of interpreting phenomena, organising knowledge and telling the story of a city.
San Michele in Bosco: the tower that gets bigger as you move away
For the final stop, head up into the hills to the complex of San Michele in Bosco, one of Bologna’s most scenic viewpoints.
Inside the complex, now home to the Rizzoli Orthopaedic Institute, a monumental corridor known as the Manica Lunga (“Long Wing”), measuring around 162 metres, ends in a window perfectly aligned with the Asinelli Tower, approximately 1,407 metres away.
And this is where perspective plays a curious trick: as you move away from the window, the tower appears to grow larger; as you move closer, it seems to shrink.
This is the famous “telescope” of San Michele in Bosco, an optical illusion that challenges the way we perceive distance and size.
The tower, of course, does not actually change. It is our perception that is deceived by the perspective and geometry of the corridor.
Please note: before visiting, it is advisable to check access arrangements for the “telescope” corridor.
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