The Pantheon

Of all the sights in Rome I wanted to see during our trip to Italy last November, the Pantheon was at the top of the list. It is perhaps the best-preserved structure of ancient Rome, having been in more-or-less continuous use (as a temple or a church) since it was built around 125 AD. It has been significantly studied and has had a significant influence on western architecture.

The Pantheon's dome remains an engineering marvel, remaining the world's largest unreinforced concrete dome almost two thousand years after it was built. The dome's thickness tapers as it rises, and lighter materials (e.g. pumice) are used in the concrete towards the dome's top. Recent research suggests Romans may have also used a special ingredient in their concrete that allows it to withstand the test of time:

[Researchers] found that white chunks in the concrete, referred to as lime clasts, gave the concrete the ability to heal cracks that formed over time. The white chunks previously had been overlooked as evidence of sloppy mixing or poor-quality raw material.

"For me, it was really difficult to believe that ancient Roman (engineers) would not do a good job because they really made careful effort when choosing and processing materials," said study author Admir Masic, an associate professor of civil and environmental engineering at the Massachusetts Institute of Technology.

"Scholars wrote down precise recipes and imposed them on construction sites (across the Roman Empire)," Masic added.

At the dome's center is the oculus, an opening that lets natural light into the interior space. It also lets in rain, which is why the center of the building's floor was roped off the drizzly afternoon we were able to enter so people wouldn't slip on the slick terrazzo.

In addition to serving as a temple and a church (masses are still held there), the Pantheon is also a mausoleum: two of Italy's kings are entombed there.

Since it is an operating church, the Pantheon is free to enter. However, in order to manage crowds on weekends reservations are required to enter. We made our visit on a dreary Tuesday, and I finally got to take a selfie underneath the ancient dome I had first learned about as an architecture student over thirty years ago.

The Pantheon was only one of many significant landmarks we saw during our three days in Rome last November, yet we felt like we barely scratched the surface of the city. You could spend an entire month in Rome and not see everything!