Likely placement
of scaffoldingAt the top, the wall reaches a
maximum angle of 60 degreesBrickStoneVertical bricks are arranged at
an angle to the center
60°
Vertical bricksInner
cap1122THE IDEA OF BUILDING the dome without
a wooden structure to support it during
the construction process was an unusual
technical challenge in 15th-century Florence.
Brunelleschi figured that by employing the
correct techniques, he could construct a
building capable of bearing its own weight
without collapsing. He used four main strategies
to achieve this. First, both the inner and outer
domes are divided into two sections. 1 The
lower section of each is built in stone and rises
from the drum to approximately 47.5 feet high.
The upper section is made of brick. Its thickness
tapers as it rises to reduce the load on the lower
rings. The next strategy 2 used a herringbonearrangement of bricks that anchored each new
ring of bricks into the ring below it, preventing
the pieces from falling off in the process. A third
strategy placed the stone blocks and bricks so
they were not totally horizontal, but gradually
inclined toward the interior of the dome. This
strategy, though apparently risky, maximizes the
surface friction between the different layers of
the construction and prevents the interior pieces
from dislodging, because they have nowhere to
lean. Finally, Brunelleschi’s fourth strategy built
interior ribs to connect the inner and outer layers
of the dome, as well as vertical brick and stone
arches that form a kind of cagework locking the
whole structure together.LOOK! NO PROPS
Opus Spicatum
The herringbone brickwork (in Latin, opus
spicatum) is a technique that has been used
since ancient times for decorative purposes.
Brunelleschi, however, also exploited
it for a structural purpose. The oblique
herringbone arches of vertically placed
bricks divide the horizontal brick rings into
bookended segments and anchor each ring
to the one beneath. Once a horizontal ring
was finished, new herringbone bricks were
placed for the next layers to tessellate with.
FERNANDO BAPTISTA/NGS