4/27/2017.   Cloudy, becoming rainy with heavy showers.   55F/70F

Cheryl and I had not been to Rome since our trip in 1994 when our daughter Amanda was 10, which was over 20 years ago. The question was: do we need to go there again? I concluded that if we were on a trip to see the greatest engineering works of the world, it would be a good idea to visit Rome again and pay more attention to the ancient engineering than we did in 1994.

The Santa Maria Hotel just across the Tiber from downtown Rome turned out to be a most charming complex consisting of a converted 500-year-old cloister arranged around a couple of courtyards … very old yet renovated to give the rooms all the modern conveniences. It was all operated by a group of very friendly ladies. The complex was surrounded by quintessential Italian apartment buildings towering over the courtyards with their faded paint, balconies with potted flowers, shuttered windows, orange trees, and bougainvillea growing over the front gate.

Photo 4984, the Hotel Santa Maria courtyard

Since we only had one full day for touring, we opted to walk around the center of Rome rather than take one of the more distant bus tours such as to Pompeii. It turns out that downtown Rome is so compact that it really doesn’t require a tour bus to get around – you can easily see the prime sights on foot.

So off we went to take in some of those iconic main sights of central Rome some of which we had never seen before. Armed with a map of the city from our hotel, we found our way out of the maze of alleys from our hotel to the Piazza Trilussa, then across the Ponte Sisto pedestrian bridge over the Tiber River, and about 12 more blocks to the #1 item on our list: the Pantheon.

The Pantheon is the best-preserved structure in Rome from ancient times … it dates from about 126 AD in its current form, built during the reign of Emperor Hadrian. It is little short of amazing in its technical mastery of the concrete construction of its dome, and in its management of lateral forces. The original Pantheon (i.e. “temple to every god”) was commissioned by Marcus Agrippa in around 27 BC during the reign of Augustus Caesar, but that building was destroyed in 80 AD by one of the periodic fires that plagued Rome. The re-constructed second Pantheon suffered the same fate as the first – destroyed by fire – so what we see today is its third incarnation.

We approached the building from the back side, and at first it was hard to tell that it was the Pantheon … it had mostly brick walls, not stone, and had all kinds of odd irregularities such as walled up arches or doors to nowhere.

Photo 1816, the undistinguished-looking back side of the Pantheon

There was a retaining wall at street level supporting the street at its current level dropping down 20 feet or so which showed that the level of the city, similar to Jerusalem, had been much lower at one time, and that the rubble from much destruction and rebuilding over the centuries had built up the street level considerably.

Photo 1829, the lower level of ancient Rome vs. the street level today

We walked around the building counterclockwise until we reached the colonnaded rectangular entrance portico on the north side.

Photo 5034, C&S at the north portico of the Pantheon

Before even entering the Pantheon, consider the columns of the portico — a wonder in their own right. The columns are 40 feet tall made of single pieces of solid granite weighing 60 tons each, quarried in Egypt, and dragged some 60 miles to the Nile to on sledges. They were floated down the river, then transferred to ships for the trip across the Mediterranean. Once in Rome and up the Tiber, they still had to be dragged nearly a half mile to be erected at the sight.

It’s startling that a building that looks so rough on the outside could look so refined on the inside with its lovely marble floors, exquisite interior stone carving detailing, and the coffered dome ceiling – all original construction.

Photo 1871, Pantheon interior, entry and oculus

Indeed, seeing all the remnants of Imperial Rome around town in falling-down ruins, it’s hard to believe that this building is from the same era – its interior is so gorgeous and completely undamaged from nearly 2,000 years of continuous use. Clearly no expense was spared in its construction; the detailing is beautiful – a complete delight to the eye.

Photo 1887, details of stonecarving in the Pantheon

We are left to imagine how grand the exterior of the building must have been with its original outer covering of white marble, but at least this gives us a look at the underlying brick structure to see how it was built.

The Pantheon is a fascinating engineering specimen – it is far more structurally sophisticated and complex than any other major Roman structure I am aware of such as the Colosseum, the aqueducts and the bridges that one sees around the former Roman Empire with their short circular arches. The main portion of the building is circular and the roof consists of a concrete dome built with no steel or iron reinforcement, which of course had not yet been developed at that time. Concrete had been used in more crude forms earlier eras, but the Romans greatly improved it, and used it extensively in their structures. For some perspective on the scale of the Pantheon, the diameter of its rotunda is considerably greater than the diameter of the U.S. Capitol, which is “only” 96 feet compared to the 142 foot diameter of the Pantheon. The Pantheon is STILL the largest unreinforced concrete dome in the world. In my opinion, it was an amazing feat of engineering to build a building that was strong enough to survive 1,900 years, outlasting most its contemporaries that were destroyed by war, earthquakes, religious fervor, or the elements!

As non-engineers may not be aware, concrete has high strength in compression, but practically no strength in tension. That is why concrete structures must be reinforced with steel reinforcing bar to provide the tensile strength that concrete lacks, where tension occurs. Although in Roman times rebar had not yet been invented (it did not come into use until MUCH later: circa the 1850s), the Romans were clever enough to build the Pantheon dome with almost no tension in it. Built correctly, domes have mostly compressive loads, but the Romans also helped the situation by making the concrete in the lower portion of the dome with stronger and heavier aggregate (where the most strength was needed) and used lighter concrete made with pumice aggregate in the upper portions of the dome to reduce the overall weight of the structure to be carried. The oculus (i.e. the open circular skylight at the top of the dome) further lightened the dome, in addition to providing light to the building interior. And the coffers (box-shaped voids on the interior of the dome) also reduced the weight of the dome. (Source: a very readable and interesting article: “The Pantheon” by David Moore, P.E., 1995, web reference: http://www.romanconcrete.com/docs/chapt01/chapt01.htm. )

One thing that puzzled me about the dome of the Pantheon was how it resisted the outward force of the dome resulting from the weight of the dome trying to push down and flatten out. A little study on the matter indicated that “brute mass” was the answer. That is, the walls supporting the dome are so massive (about 20 feet thick) that their sheer weight resists the outward force exerted by the dome.

The Hagia Sophia in Istanbul aside, the knowledge of how the ancient Romans built domes was lost for about a thousand years through the Middle Ages after the decline of the Roman Empire. It wasn’t until the 1400s that such knowledge was re-learned. The Duomo cathedral of Florence sat with an open rotunda for about a hundred years because no one knew how to build the large dome that had been planned for it. Enter the brilliant but untrained amateur Filippo Brunelleschi who devised a scheme of supporting ribs, an iron chain tension ring at the base of the dome, and interlocking bricks in the dome … all built without supporting scaffolding. The Florence dome, completed in 1436, is still considered a technical marvel today. How it was done is still unknown since Brunelleschi kept no notes on how he did it.

Photo 3738, the Duomo cathedral of Florence, Italy, from our 1994 visit

Cheryl and I spent a good hour in the Pantheon each of us getting photos from every conceivable angle, and just generally admiring this magnificent structure.

From the Pantheon, we walked some more narrow back streets to the Via Del Corso and the Piazza Venezia where the huge white monument to Victor Emmanuel II is located. It is sometimes referred to as “the typewriter” because of its rather boxy appearance. Victor Emmanual II is considered the father of united Italy … in 1861 be became first king of a united Italy since the 6th century.

We skirted the big white monument passing by a big open area of partially excavated ruins and onto the Via Dei Fori Imperiali which from its higher level gives a great broad view of the Roman Forum, which sits at the lower former level of ancient Rome. The Forum was the hub of social and political life at the heart of the Roman Empire – the site of processions of returning victorious armies, where the Roman Senate was located, where the debates of the day were held, where Julius Caesar was murdered, and, next door: the Colosseum. That’s a quite a concentration of history in a small area!

Archeological excavations didn’t begin until the 1800s and are ongoing today with new discoveries continuing.  Later excavations have led to the conclusion that the city is older than previously believed, dating back to the 8th century B.C.  To give you an idea of how this area was regarded through the Middle Ages down to the 1800s, it was referred to as the Campo Vaccino or “cattle field“, because cattle grazed in this generally ignored part of the city!  It’s not ignored any longer as the Forum draws around 4.5 million visitors a year.

Photo 1944, heart of the Roman Forum looking southerly, Palatine Hill far L, Senate House far R

Photo 1945, the Roman Forum, the Curia Julia (Senate House) circa 44 BC, Julius Caesar’s era

We contemplated the sight of the Forum for a while from the panoramic viewpoint of the Via Imperiali, then moved on to visit the Colosseum, built starting in 72 AD under Emperor Vespasian, and completed in 80 AD under the Emperor Titus. The day of our visit was a cool showery day which was a good thing because the lines were short, but the bad part was that light on the cloudy day was not great for photography. More than on our previous trip, this time I was much more interested in how the Romans arranged their circular arches and vaults of the Colosseum everywhere in multiple directions wherever they need to span a space, and cleverly put it all together to achieve this great amphitheater.

Photo 1968, north exterior of the Colosseum

You may recognize from your high school history class the form of the column capitals (top of columns) borrowed from the Greeks: the plain Doric style on the first tier, the scrolled Ionic style on the second tier, and the leafy Corinthian style on the third tier, which are incidentally all strictly decorative with no structural function.

The system of passages and tunnels under the floor of the arena was not part of the original construction, but was added later. I have always wondered how flooding the arena to depict sea battles could have been done with all those tunnels underneath, but that would have been done before the tunnels were added. There was a nearby aqueduct that would have made such flooding possible.

Photo 2015, the Colosseum interior, arena floor partially reconstructed

In Roman times, the Colosseum was used for various types of events including gladiatorial contests, hunting exhibitions using wild animals, re-creations of great battles, or scenes from mythology. Such shows were typically staged by wealthy individuals or families as a show of their power and prestige, and were highly popular. It was also used for public executions where prisoners condemned to death, among other methods, would be turned loose in the arena naked without weapons to be torn to pieces by wild animals. Tradition holds that the Colosseum was the place of mass martyrdom of Christians in its earlier years. However, there is controversy about that due to a lack of historical records of the time, due to inconsistent veneration by the church, and other reports indicating that such things were more commonly done at the Circus Maximus nearby.

Down over the centuries, the Colosseum was not always revered as a monument to Imperial Rome. At various times it was used as a cemetery, a place for houses and workshops, as a castle, and the home of a religious order for several centuries.

About half of the outermost wall on the south side is missing; it was sitting on a section of less stable ground. It turns out that the site of the Colosseum was previously the location of Nero’s palace which included a lake, hence the softer ground on one side. The outer wall collapsed during a severe earthquake in 1349, after which the stone rubble was carted away and reused for the construction of churches, palaces and other buildings elsewhere around Rome. A partial reconstruction of the arena floor had been built since our 1994 visit, but otherwise it looked much the same. It is not immediately clear how much of what you see there is original, and how much is reconstructed – which would be interesting to learn more about.

By the time we finished making a loop of the upper level of the Colosseum, a serious rain started to fall. We took a last look then made a dash to return to the hotel, passing by the Palatine Hill and the Circus Maximus where chariot races and other events were held.

Photo 5172, the long Circus Maximus, site of the chariot races, et al

Just past the Circus Maximus we were back to the Tiber, and we walked upstream along the left bank back to the Ponte Sisto where we started earlier. Back at our room, we checked in for our flight to Geneva the following day, and topped off the day with a lovely dinner at an outdoor café in the Piazza Santa Maria a couple of blocks from our hotel.

Looking back on it, I’d have to say that we loved Rome: the history, the piazzas, the outdoor cafes, the ruins everywhere, our hotel, the narrow streets, the cobblestones, the churches … and we barely scratched the surface. Our visit plus all the subsequent reading has left us with hunger for another trip to see much more, learn much more, travel farther afield, to take more tours and take time to better understand what we are seeing and soak it all in. Late April was a good time to be there. The cool weather, smaller crowds, and even some rain made it vastly better than the oppressive heat of mid-summer that we experienced in 1994.