The Ancient Romans were master architects, builders, and innovators. That we can still see the remains of many 2,000+-year-old structures is a testament to the Romans’ skill and to the materials they used. And also to the happy fact that in subsequent millennia, rather than be destroyed, many ancient buildings and structures were built over or incorporated into other buildings, or simply left where they were as the effort involved in removing them would be too great. Here is one example I’ve always enjoyed seeing: apartments built right into and around the ruins of the Baths of Agrippa near the Pantheon:
In contrast, I am certain that in 2,000 years, there will be nary a trace of my house here in the Midwest or any of the modern buildings nearby. So, how did the Romans make structures that have lasted so long? The answer is that they made excellent concrete and great bricks, and combined the two in various ways to construct extremely strong and long-lasting walls and other structures.
Of course, walls and buildings were also built with blocks carved from rock. In Rome, some of the earliest examples you can see are “dry walls,” built with blocks of volcanic rock called tufa without any mortar between the blocks. This technique of using blocks is called opus quadratum (also, ashlar or cuboidal masonry):
If you are walking around Rome and see these types of tufa-block walls, you can be sure they are quite old. They deserve a nod of appreciation, because cutting large blocks cleanly and evenly, hoisting them, and placing them perfectly with just their weight and position to keep them in place — that is a feat requiring a lot of hard work and skill.
Building techniques began to change in the second century BC, when the Romans discovered they could substitute volcanic ash (pozzolana) for the sand in concrete mixtures, yielding much stronger and more weather-resistant concrete. This super concrete turned out to be a perfect material for the inner core of walls (opus caementicium). Plus, it did not require as much hard work or skill to make, compared to the large block walls. The idea was that the concrete core would be covered (ie, faced) with stone or brick, and then, depending on the structure, faced again with stucco, paint, or polished stone veneers like marble.
One of the first ways of using this concrete core involved a construction technique called opus incertum: randomly inserting irregularly shaped, uncut stones and/or small tufa blocks into the concrete. This technique was used in building the Porticus Aemilia, a storehouse complex built in 193 BC along the Tiber river by Testaccio:
Though fired bricks had been around for a long time, the Romans did not really begin to use them significantly until the cusp of the first century AD. Two of the first structures to be made of fired brick in Rome were the Theatre of Marcellus (Teatro di Marcello) and the Tomb of Caecelia Metella on the Appian Way. The Teatro di Marcello was completed in 13 BC; miraculously, it still has its facade, though apartments were built on top of it in the 16th century. The Tomb of Caecilia Metella is thought to have been built somewhere between 30-10 BC.
After these two structures were built, fired bricks began to be used all across the Roman Empire, in various ways. The most basic was a technique that involved facing the concrete core of a wall with courses of brick. It was called opus testaceum. The cut-away section in the photo below shows an inner concrete core and brick facing, from a wall at Portus, the ancient port of Rome, built around 50 AD. (Portus is about 35 minutes from central Rome, near Fiumicino Airport, and is definitely worth a visit if you can make it there.)
Though bricks had come into fashion, tufa and other materials were still used as building materials. The photo below is of a section of the Aurelian Wall (270-275 AD) made with both brick and tufa. The technique used is called opus vittatum (ie, banded work, when the bricks and tufa are placed in alternating rows):
Roman bricks came in different sizes: round, square, oblong, triangular, or rectangular. And walls were also built in different patterns. A pattern of pure brick rows (courses) was called opus testaceum, as mentioned above. Though it is hard to see, the skinny flat bricks used in these types of walls were often triangular, with the longest side lined up on the outside of the wall and the pointy side of the brick embedded in the concrete. A diamond or net-like pattern was called opus reticulatum. It consisted of small tufa blocks carved like little pyramids, with the square base being visible and the pointy part embedded in the concrete. When two techniques were used together, that was called opus mixtum.
The photos below show a wall in the Portico of Claudius, at Portus. On the right side of each photo is a section of opus testaceum (OT), ie, uninterrupted rows of bricks. The left part of the photo shows a section of opus mixtum (OM) consisting of a couple rows of brick (opus testaceum) interspersed with diamond-shaped sections of tufa blocks (opus reticulatum, OR).
Sometimes, the opus reticulatum was made with a combination of brick and black basalt instead of tufa to achieve a more distinct polychrome coloring, as in the first photo below from Ostia Antica (which is also an example of opus mixtum). Fun fact: The black cobblestones of Rome are also made out of black basalt.
Sometimes you will see brick arches in the walls. They are called relieving arches and they were used on tall walls, and above doors or windows or other openings, to help distribute weight and maintain structural integrity. The square holes you often see, too, are where the scaffolding was inserted when the wall was being built. They are called putlog (or putlock) holes. Other holes are where the exterior facades were attached.
I hope these notes on bricks, stones, structures, walls, and holes will help as you walk around Rome, take day trips, or find yourself seeing Roman ruins anywhere else in the world.
I’ll sign off with a question about a longstanding mystery. I have always loved the look of this wall in the Cortile Biblioteche at Hadrian’s Villa in Tivoli (about 40 min. drive from Rome). But I have never been able to figure out why it was constructed this way, with pointy bricks sticking out. So if anyone knows, please do tell!
Perennial Pastimes 