#31 Brunelleschi & The Dome II

When Bruno – or Pippo was he was known to his friends (short for Filippo) went to Rome, after the embarrassment of the Baptistery doors competition, it wasn’t the Rome of Augustus.

At its height, Rome’s population was one million people.

When Bruno arrived there, it was less than 20,000, thanks to the Black Death of 1348.

1/50th of its heyday.

Can you imagine what that would look like?

Rome had shrunk into a tiny area inside its ancient walls retreating from Seven hills to huddle among the few streets on the bank of the Tiber across from Saint Peters whose walls were in danger of collapse.

It was full of wild animals and beggars everywhere.

There were livestock grazing in the forum which was now known as the field of cows.

The temple of Jupiter was a Dunghill and both the theatre of Pompey and the mausoleum of Augustus had become quarries.

People would come and take the building materials for use in other buildings some as far away as England.

Statues were lying around in rubble everywhere.

Some through neglect, but others had been deliberately destroyed by Christians who saw them as pagan idolatry.

The true nature of Bruno’s visit to Rome was unknown even to Donatello, his travelling companion.

Bruno would walk around studying ancient ruins while pretending to be doing something else, and making notes in a secret cipher in his notebook.

This was common practice in those days.

There was no such thing as copyright or patents.

Manetti claims Bruno was measuring heights and proportions of the buildings.

Where did he get this idea?

And how did he measure them?

Might have used a rod.

Or he might have used the mirror trick.

Both of these methods were discussed in Leonardo Fibonacci’s book Practica Geometriae.

The mirror trick – you position a mirror facing the object you want to measure, then walk backwards until the top of the object appears in the center of the mirror.

Then its height is arrived at by multiplying the distance between the object and the mirror by the height of the observer divided by his own distance from the glass.

Or he could have employed a quadrant.

So you know how that works?

Get a quadrant – like a protractor – and mark it off at a 45 degree angle.

Make sure it’s level to the ground and walk backwards from the object you are measuring until the top of it is in line with the 45 degree marker.

You then have an isosceles triangle.

has two sides of equal length

The distance from where you are standing to the base of the column would be equal to the height of the column.

Or you could just ask Siri.

He was measuring the columns and pediments to determine the measurements specific to the three architectural orders – Doric, Ionic and Corinthian.

Devised by the Greeks, refined by the Romans.

Governed by precise mathmatical ratios

A series of proportional rules that regulated the aesthetic effects.

For example the height of a Corinthian entablature is a quarter of the height of the columns on which stands

While the height of each column is 10 times its diameter

The entabulature is the upper part of a classical building supported by columns

commonly divided into the architrave (the supporting member immediately above), the frieze (an unmolded strip that may or may not be ornamented), and the cornice (the projecting member below the pediment).

The Doric is most easily recognized by the simple circular capitals at the top of columns.

It’s the earliest form.

The Ionic capital is characterized by the use of volutes, a spiral, scroll.

The Corinthian is the most ornate of the orders.

This architectural style is characterized by slender fluted columns and elaborate capitals decorated with acanthus leaves and scrolls.

Here’s how to remember them.

Doric rhymes with Boring.

Corinthian is the longest word and is the most developed column.

Ionic is ironically in the middle.

portico of the Pantheon the Corinthian.

The Colosseum makes use of all three: Doric on the lowest level, Ionic on the second, and Corinthian at the top.

So why did Bruno go to Rome?

To get to the other side.

He grew up looking at the homeless top of the Duomo.

By the beginning of the 15th century, after a hundred years of construction, the structure was still missing its dome.

And when he lost the competition for the Baptistery doors to Ghiberti, he said to himself “I’m going to build that dome.”

And there would have been lots of domes to see in Rome.

After large parts of the city were burned in the fire of 64, Nero had established regulations that widened the streets, controlled the water supply, and—most vital from an architectural perspective—restricted the use of inflammable building materials.

The Romans therefore started to use concrete, a relatively new invention, in their buildings.

The secret of Roman concrete was in its mortar, which contained a volcanic ash made available by active volcanoes such as Vesuvius.

Combined with lime mortar, it resulted in a strong, fast-setting cement to which they added small broken stones.

Unlike conventional mortars made from quicklime, sand, and water, which set only when the water evaporates, “pozzolana concrete” (as it is known) combines chemically with water so that it cures swiftly, even underwater.

Although various Roman baths had been vaulted in concrete since the first century B.C.E, extensive and inventive use of concrete arches and domes was made only after the fire of 64.

The history of domes commences, effectively, with the opportunities created by this great conflagration—one that the Romans believed was either the work of Nero himself or else that of the gods.

Or Christians.

The Domus Aurea Golden House of Nero had a concrete dome on an octagonal room.

Just like the Duomo.

Although Nero’s dome was much smaller.

And of course Of even more interest to Filippo would have been the Pantheon, the emperor Hadrian’s temple to the gods of all the planets, executed between A.D. 118 and 128.

Not only the largest dome ever built, and still standing 1300 years later, it had no visible signs of support, it seemed to defy the laws of nature.

The architects of the Pantheon faced the statical problems encountered by builders of all domes: how to counteract the forces that act on any vault.

These forces are separated into “push” and “pull” energies, known respectively as compression and tension.

All elements in a building—its columns, arches, walls, roof beams—are subject to one or other of these actions: their stone or timber beams are compressed from above (which causes them to shorten) or pulled from the side (which causes them to stretch).

An architect must design a structure that will counteract these pressures by playing them off against each other—a game of action and reaction—and channeling them safely to the ground.

The first type of pressure does not create insurmountable problems for an architect.

Stone, brick, and concrete all possess such enormous compressive strengths that buildings can be raised to colossal heights without the blocks of stone crushing at the base.

The stones in a dome, however, are not only crushed from above but also thrust outward by the pull energy known as “hoop stress,” in the same way as the rubber of an inflated balloon will bulge outward if one compresses it from above.

The classical example (and namesake) of hoop stress is the tension applied to the iron bands, or hoops, of a wooden barrel.

The problem for architects is that stone and brick do not respond nearly so well to this lateral thrust as they do to compression.

The Romans seem to have possessed some understanding of the structural problems created by tension and compression, and they attempted to solve them by making extensive use of the new pozzolana concrete.

Where the horizontal stress is greatest, at the base of the dome, the concrete wall of the Pantheon was built to a massive thickness of 23 feet.

It then tapers to only two feet at the top, at which point a round window or “oculus” is left open.

Five thousand tons of concrete were poured in horizontal layers on to wooden formwork, but at the top of the dome lightweight aggregates such as pumice and, more inventive still, empty amphorae (clay bottles used for shipping olive oil) were added to the concrete in place of stone in order to reduce the load.

The inside of the dome was also coffered – sunken panels in the shape of a square, rectangle, or octagon –  which not only lightened the load still further but also added a decorative feature that has since been extensively imitated.

So the Pantheon dome offered proof that a huge dome could be self-supporting.

The height to the oculus and the diameter of the interior circle are the same, 142 feet (43 m).

The dome on the Duomo would have to 44 meters (144 ft).

Slightly larger.

Arnolfo di Cambio had always intended to cover the enormous space of some 45, 50 metres with a dome.

The problem was that no one really knew how to place a dome over such a wide space.

In 1366, the board of the Opera del Duomo – the “works commission”  founded by the Republic of Florence in 1296 to oversee the construction of the new Cathedral and its bell tower – orders the construction of two dome models.

One is a quite traditional design by master building Giovanni di Lapo Ghini.

The other model, which would end up winning, was by a group surrounding Neri di Fioravanti.

Di Lapo Ghini’s model was based on the aerial arches and buttresses that were commonplace in Gothicism.

This wasn’t particularly popular in Italy.

Quite a number of Italian architects saw aerial arches as a rather ugly aid.

What was remarkable about the winning model is that it was not being supported by aerial arches.

And, quite unusually so, the dome would become double-walled.

Fioravanti’s model was deemed the best during a referendum.

The model was placed in the aisle of the Duomo for quite some time and after Brunelleschi had built his dome it became a urinal.

Despite Neri di Fioravanti’s model, no one really knew how to build that kind of dome.

It’s thought that Bruno returned to Florence probably in 1416 or 1417