The Pantheon in Rome is a rare ancient building because it has resisted the decay of time so well. One reason it is such a treasure is that it is the only intact example of architecture of the time of that size, age and span. The ability of The Pantheon to hold up for centuries is no accident - rather, it reflects a genius of engineering skill.



Many designers have copied and even equalled the amazing design of this building, but none have done better at introducing true innovation in architecture as the Pantheon did. This is even more phenomenal when you take into account that the building was designed in 125 AD under the Roman emperor Hadrian.

The heart of the design genius is as simple as it is elegant. It simply employs a circular construction with a rectangular entrance. That entrance displays all the characteristics of a Greet portico that utilizes a triangular pediment that perches atop granite columns. The Corinthian supporting columns are arranged with eight 39 foot supports at the front of the gateway, and two sets of four supports that the visitor passes through before entering the circular rotunda of the Pantheon proper. Then the rectangular design is used to link this portico design to the rotunda.

The geometric simplicity of this design also displays many layers of sheer architectural brilliance.

For example, the massive dome of concrete that is on top of the round central component is of such elegant design and of such high quality of construction that anything less in the design of this dome would have collapsed under its own weight.

That dome is nothing short of massive. At 142 feet in diameter, the Pantheon dome is 46 feet larger than the dome over the White House. At the crown of the dome there is an opening known as the oculus that is 25 feet across. The fact that the dome does not compromise the building and continues to survive after 2000 year is in part due to the design of that oculus and the composition of the dome.

It's easy to think that the opening in the center of that large oculus is just for artistic design. But it has an important job of reducing the weight of the dome. It is also perfectly balanced to distribute the stress of the dome's weight around its circumference. This makes the dome as resistant to being crushed as a bicycle wheel that we are familiar with.

Along with helping to keep the dome aloft, the oculus allows in a soft natural light which illuminates the interior beautifully. It also allows in rain, but the designers planned the slope of the floor so water flows naturally away from the center to a drainage system in the perimeter so a sprinkle does not create a significant problem.

The talent of the designers is also on display in the tapering steps of the dome. That dome is an amazing 20 feet thick at the base of the structure and 7.5 feet thick at the oculus. The composition of the dome is also a part of the balance that keeps it aloft because the lower parts are made of heavier materials and as it rises to the peak, the material that was used is lighter. This simple design plan seems obvious but many architects down through time and to this day do not use such simple design methods to replicate the success of that dome.

The outcome is that now over 2000 years from when the Pantheon was built in Rome, it is just as solid as any new building in the city. Consider as well that this construction plan was executed without the use of high technology or modern tools and machines we take for granted in our modern age.

Now you add to that limitation the fact that the creators of the Pantheon had to work with relatively "primitive" means of transportation and the success is even more impressive. Every pound of building materials for this amazing building had to be floated to the site down the Tiber River and then laboriously moved to the building site by cart using nothing more than human or animal power.

The massive doors of bronze also testify to design genius because while there have been renovations to keep them looking good, they have never needed any structural help. They have worked flawlessly for two millennia and done so despite the fact that the Pantheon was built on soft marshy land.

The weakness of the ground under the Pantheon is similar the Leaning Tower of Pisa which has had numerous preservation projects that have lasted decades to keep it from falling. Also by comparison, the Greek Parthenon is a stunning building in every respect but 2000 years past when it was created, it is in shambles compared to the Pantheon. It just goes to show how magnificent a job the designers and builders did when creating the Pantheon.

In the eighth century the Roman Pantheon became a church, and it is a functioning house of worship down to modern times. Unlike other buildings of similar age, the Pantheon continues to be as much a working building as it was the day it opened.

It is such a design marvel that the Pantheon has become a template for great engineering for numerous modern projects including the University of Virginia's Thomas Jefferson Rotunda and the British Museum Reading Room.

That background makes your time with the original Pantheon even more fascinating.