Presentation on the Pantheon Dome

1. PANTHEON DOME
Oldest Unsupported/Unreinforced Dome in the World

2. ORIGIN
 Commissioned by Emperor Hadrian
 The word “Pantheon” loosely translates to
“all of the gods”… the Pantheon serves as a
temple to the Roman gods, the dome being
the divine feature
 Built between 118-128 A.D.
 1,887 years old (still in use today)

4. DOME
 Depth from dome’s apex to floor is exactly equal
to the width of the dome (142.4 ft)
 Meaning: the rotunda (round floor beneath
dome) and dome are configured in accordance
with a perfect sphere
 Because of no reinforcement to keep the dome
from trying to “push” or “flatten” out, Romans
built 20 ft thick walls to serve as buttresses for
the dome
 Based on the “arch” concept

6. WEIGHT OF DOME
 The most critical issue Roman engineers
faced was the dome’s own dead weight
 Roman engineers needed a material with a
larger strength to weight ratio than traditional
stone. Answer: concrete
 Strength was not a central issue in the
design, but rather the weight and stresses
associated with the material used

7. ROMAN CONCRETE
 Very strong by modern standards
 For the Roman engineers, the concrete was
still too heavy, so they needed to develop
ways to reduce the amount used
 Roman engineers conducted a stress
analysis of the dome and determined that the
compression stresses were smaller towards
the top. Solution: pour a progressively
thinner layer of concrete

8. ROMAN CONCRETE (CONTINUED)
 Romans relied on the chemical reactions that
took place between the lime and pozzolans they
added into the mix to strengthen their concrete
 Pozzolans – volcanic ash found in and around
Puzzuoli Bay near Naples (varies in dome)
 Roman engineers used small hollow jars called
amphra as aggregate… used to displace
concrete to make mix lighter

9. ROMAN CONCRETE (CONTINUED)
 Coffers – ingenious Roman innovation which
removed an array of concrete sections…
made the dome lighter and more appealing,
all while maintaining thick sections to serve
as reinforcement
 Oculus – used to distribute the stresses
acting on the dome’s weakest point along a
rounded perimeter… also serves as an
aesthetic feature

11. REFERENCES
 Rome: Engineering an Empire
 https://www.youtube.com/watch?v=C5obOUDy
Q5s
 The Secrets of Ancient Roman Concrete
 http://www.history.com/news/the-secrets-of-
ancient-roman-concrete
 The Pantheon
 http://www.romanconcrete.com/docs/chapt01/ch
apt01.htm