The
Pantheon, one of the most impressive buildings
in Rome, was rebuilt in A.D. 117-125 by Emperor
Hadrian to replace an earlier temple designed
by Agrippa in 27 B.C. The original rectangular
temple, consisting of sixteen single granite columns,
became the porch for the newly devised dome structure.
Once the Romans learned to use concrete, they
were able to mold on the ground their rounded
tops for their buildings and hoist them into place
on top of a rotunda. The Pantheon is just such
a structure with an opening at the center top
of the dome. Because this opening is not covered,
the floor is slightly concave with a drain at
the center so as to catch the rain when necessary.
The Pantheon was originally dedicated as a
temple to all gods, hence the name.
