Every so often, someone, while discussing ancient history, will tell me how fortunate we are to be alive today as opposed to say, 2,000 years ago. I actually hear this fairly frequently. The reasons behind this preference for the now, as opposed to the past, vary. I can certainly understand why the average American might feel this way. After all, at no time in recorded history has a people enjoyed greater freedom and prosperity than those who have lived in the United States during the past century. Of course, as the bumper-sticker says, "Freedom is not free." To stay free a people must resist the forces that strive to grasp power and enslave them. The history of humanity is largely a history of darkness enlightened only occasionally by brief moments of true, responsible freedom.
Others take a more progressive view, assuming human existence always moves forward to something better. One friend, a scientist, actually claimed we are far more intelligent today than those who went before us. "Like everything else," he explained, "IQs have no doubt increased as we continue our upward evolution." He wasn't happy when I challenged him by reciting a few basic historical facts. For example, the number of people slaughtered in wars since 1914 exceeds the total killed in warfare through all previous recorded history. Does he believe, then, killing people by the millions is a valid indicator of a higher IQ and continual upward evolution? I had other questions. He disliked them all.
Another acquaintance, like me educated as an engineer, took a humbler approach and admitted that knowledge is a continual building process in which we add our own advances and insights to those passed on to us. In this he mirrors the comment of Bernard of Chartres, who in the early 12th century claimed:
"...we [the Moderns] are like dwarves perched on the shoulders of giants [the Ancients], and thus we are able to see more and farther than the latter. And this is not at all because of the acuteness of our sight or the stature of our body, but because we are carried aloft and elevated by the magnitude of the giants."
I suppose, for an engineer, such an attitude makes sense. Progress in engineering, which is really the application of science and technology to current needs and problems, builds on that which has been learned and tested over the centuries. This can, however, result in a kind of temporal bias, in which that which came before is generally considered inferior.
Indeed, we can argue that in many fields -- the arts, for example -- exactly the opposite is true. I would gladly argue that any fugue and prelude by Bach, a Bethoven symphony, or a concerto by Mozart or Vivaldi, by any reasonable measure far surpasses most of the music to which we are subjected today. Some of today’s music is quite good, but very little of it is great. I believe this applies, too, to many of the visual arts. And interestingly, it seems also to apply, at least in some instances, to engineering. The Pantheon in Rome is a perfect example. Here’s an aerial view of the Pantheon, thanks to Google Earth:
On our first trip to Rome, Diane and I visited the Pantheon, designed as a Roman temple dedicated to all the gods. It was built, in its final form, sometime in the early 2nd century by the Roman emperor Hadrian. By any standard it is a remarkable structure. The Pantheon is a circular building fronted by an impressive rectangular portico supported by huge columns. I took the below photo back in November 2005. Approaching the building from the Piazza della Rotonda we are almost overwhelmed by the large portico and its massive columns.
The interior, the rotunda, sits under a unique concrete dome with a central opening or oculus that lets in sunlight. The dome is still the world's largest unreinforced concrete dome, the only dome of its kind that does not need reinforcement. In the photo below we see the oculus along with part of the surrounding dome:
How big is the Pantheon? The dome's height and diameter are identical (142 ft). At its base the dome is 21 feet thick, while at the top, at the oculus, it is only about 4 feet thick. The content of the materials used to make the dome also vary with height. Concrete was a material which the Romans understood well, and as they built the Pantheon, they applied different aggregates to the concrete mix, from travertine limestone at its thick base to terracotta tiles and ultimately at the top very porous light stones like pumice. The oculus also lightens the loads on the structure where it would be weakest. And the inclusion in the dome of multiple bands of sunken panels (or coffers) further reduces the weight. These bands are visible above and also in the following photo of the Oculus.
I’m not a civil engineer but I did make my way through a course on strength of materials in which our professor waxed eloquently about the Romans’ use of concrete in building the Pantheon, the Colosseum, and many other structures. I recall his telling us that modern concrete has a limited life and usually begins to deteriorate after some decades. I think of all the bridges and interstate overpasses that have had problems in recent years and the billions we have spent to repair them and other elements of our national infrastructure. Our professor, again referring to the Pantheon, went on to say that he and his peers could not understand how ancient Roman concrete seemed to last forever. Discussing this he added that perhaps someday we would figure out the secret and catch up with Roman technology.
Well, apparently this has finally been accomplished. It seems that scientists, archaeologists, and historians have been working independently and occasionally together for many years trying to uncover the secrets of Roman concrete technology. This technology and the techniques that derived from it have resulted in some of the most enduring structures ever made. In a study published in Science Advances researchers from MIT and Harvard, assisted by others from research laboratories in Germany and Switzerland, explained what they believe made Roman concrete so durable and of such high quality. (Note: the article is quite technical, but readily understandable by all serious techno-dweebs.)
As a result of extensive examination of Roman concrete, the researchers discovered that the Roman manufacturing techniques included “key self-healing functionalities.” In other words, the concrete would continually heal itself so it wouldn’t deteriorate over time. It seems small, bright white chunks of lime — what are called “lime clasts” — are abundant in Roman concrete. These chunks of hardened lime were always thought to be mere contaminants, the result of sloppy mixing by the Romans. Everyone was certain they were certainly not essential elements of the mix. Well, not everyone. Adam Masic, MIT professor of civil and environmental engineering, had long been skeptical and decided to find out the truth. In his words:
“Ever since I first began working with ancient Roman concrete, I’ve always been fascinated by these features...The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me. If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There had to be more to this story.”
He was right. Using high-resolution imaging and chemical mapping technology they examined the lime clasts at a molecular level and discovered the clasts had been subjected to high heat, producing what’s known as quicklime. Quicklime, then, was an intentional ingredient and not a contaminant. As Professor Masic explained it:
“The benefits of hot mixing are twofold. First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked [cold mixed] lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”
The lime clasts resulting from this hot mixing process are brittle, so brittle that when the concrete starts to crack over time, the force is shifted to the lime clasts, which also begin to crack. Here’s where it gets truly amazing. These crumbling, cracking lime clasts then react with water penetrating the concrete through the cracks. This results in a calcium-saturated solution that hardens and fills all the cracks in the concrete. It then reacts with the pozzolanic materials and adds extra strength to the concrete blocks. The lime clasts, then, long thought to be contaminants, automatically heal Roman concrete whenever the forces of nature threaten to break it apart.
And so, the Pantheon, constructed almost entirely of concrete still stands strong after 2,000 years. And it only took that long for us moderns to learn the secrets of Roman construction technology. Pretty smart people, them ancients. Oh, yes, and the ancients are also the folks who, guided by the Spirit, wrote the Bible.
An afterthought: I’ve added a couple of other Pantheon photos below, just to give you a sense of the interior of this wonderful building which is now a Catholic Church. The first shows the interior empty of tourists because a special Mass was about to begin, a Mass we attended.
And here’s a photo of the Pantheon’s entrance. The doors are original, and I believe they’re the world’s largest bronze doors.
Finally, a photo I took in 2008 showing a typical crowd of tourists roaming about the Pantheon rotunda.
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