STEVEN ZUCKER: We're in Florence.
And we're standing outside of the Duomo.
BETH HARRIS: The cathedral of Florence,
and we're looking up at Brunelleschi's dome.
STEVEN ZUCKER: It's huge.
Until St. Peter's, it was the highest dome
that had ever been raised.
And in its width, it was as wide as the Pantheon.
BETH HARRIS: Almost.
STEVEN ZUCKER: If you think about the Duomo
itself had been planned in the 14th century.
BETH HARRIS: The plan was to build
a dome that had a span nearly equal to that of the Pantheon.
STEVEN ZUCKER: And of course, the Pantheon
had been built in the ancient world.
And that technology had largely been lost.
BETH HARRIS: So first and foremost,
what Brunelleschi did was an amazing engineering
achievement.
The challenge was how to build a dome
this wide without wooden centering.
Generally, when you build an archway--
and the dome is really just an arch--
STEVEN ZUCKER: In the round.
BETH HARRIS: --in the round-- you put up a wooden framework.
STEVEN ZUCKER: So this is the wood
to actually support the dome until it
can be locked in place by the keystone.
BETH HARRIS: Exactly.
So you don't even really need mortar
to hold it together because you've got the keystone.
STEVEN ZUCKER: The problem is that this was so big,
they couldn't actually get enough lumber,
and lumber that was strong enough, to hold the thing up
until they could lock it in place.
BETH HARRIS: And so there was no way
to do wooden scaffolding or centering to hold it up
as it was being built.
So how do you build this dome that inclines inward
and not have it fall down?
STEVEN ZUCKER: There's two problems.
You've got that issue.
And then you've got the problem of it wanting to splay outward.
BETH HARRIS: A dome exerts pressure not only down,
but down and out.
And so one of the biggest challenges
is how to raise the dome and deal
with that downward and outward pressure,
not cracking the walls underneath.
STEVEN ZUCKER: Now, in the ancient world,
for the Pantheon, for example, they had dealt with that
by just creating sheer bulk.
In other words, the walls got to be 10 feet thick.
BETH HARRIS: I think, actually in the Pantheon,
they're something like 20 feet thick of concrete.
STEVEN ZUCKER: But Brunelleschi couldn't do that here.
So what he's done instead is, first of all,
he made the decision to make the dome as light as possible.
And that means that it's basically hollow.
It's a double shell.
And within the shell is a staircase
that snakes around that allows one to actually get to the top.
And if you look, you can see people just below the lantern,
up at the top of the dome, taking in the view of the city.
BETH HARRIS: He also created ribs.
STEVEN ZUCKER: Which are doing a lot of the weight bearing.
BETH HARRIS: And then in between each of the major ribs, which
are visible on the outside, there
are two within that we can't see.
STEVEN ZUCKER: And those are actually locked in place
by a series of horizontals, as well.
So there's this whole skeletal structure
that's actually holding this piece together.
I think, most importantly, he was
able to develop a system where, as the dome was being raised
up, as each course of stone and brick was added,
it was actually locking itself in place.
And so it was self sustaining.
BETH HARRIS: Another way that Brunelleschi
dealt with the downward and outward thrust
was to create chains inside the dome made out
of stone and wood, locked together with iron,
like a girdle, to hold the dome in
and to counter that downward and outward thrust.
STEVEN ZUCKER: You might think of an old-fashioned wooden
barrel that has a couple of iron rings around it
to help keep the wood together.
BETH HARRIS: Brunelleschi created
cantilevered scaffolding.
STEVEN ZUCKER: That could rise as the building went up.
BETH HARRIS: And so the workmen had a place to work.
Brunelleschi also built new kinds of pulleys and hoists
to bring up his heavy, massive pieces of stone
to the top of the dome.
So he created this ox hoist, just these remarkable machines
that no one had ever seen before.
STEVEN ZUCKER: He actually even designed a special barge
to go down the Arno to be able to bring
the materials to the city itself.
If you think about the sheer quantity of material that
had to be imported, and had to be hoisted up,
and had to be put in place, it is just
this remarkable project.
BETH HARRIS: Bricks that had to be created, stone that
had to be quarried and brought here, platforms for the workmen
to work on, machines to hoist everything.
And I think it was Alberti who said something
like, what Brunelleschi did, he did without--
STEVEN ZUCKER: --without a precedent.
BETH HARRIS: Without having any example to lean on.
STEVEN ZUCKER: Utter invention.
Now, we think that Brunelleschi may have gone to Rome
and may have studied ancient architecture as well
as sculpture there.
But there is no precedent in the ancient world, even,
for what Brunelleschi accomplished here.
BETH HARRIS: Now, it's important to say that the dome is not
hemispherical, like the dome on the Pantheon.
STEVEN ZUCKER: It's actually kind of tall.
BETH HARRIS: Right.
It's kind of pointed.
In a way, it has more of a Gothic shape
than a classical shape.
But in that way, it matches the Gothic church itself.
If you look closely, you can see these exedrae,
or blind tribunes, that Brunelleschi
added around the outside of the dome.
They actually look very classical
compared to the Gothic church there.
In fact, look like Roman triumphal arches.
So there's this curious classical moment
here in an otherwise very Gothic church.
STEVEN ZUCKER: And it's a church that
is not only Gothic, but really referring back
to the Tuscan Romanesque tradition.
Especially in terms of the polychromy, the colored
marbles, which Brunelleschi also carries up into the barrel
just below the dome itself.
But ultimately, you've got Brunelleschi,
who, through his engineering genius,
is solving a problem the Western tradition had never
been capable of solving before.
How does one span this enormous space?
And in order to do it, he's surpassing the ancients
that he's even here paying reverence to.