The Tomb of Caecilia Metella is a mausoleum located just outside Rome at the three mile marker of the Via Appia.
The Tomb of Caecilia Metella is a 2000-year-old mausoleum located along the Via Appia and is one of the most popular tourist sites in Rome. The structure was marveled at by Lord Byron in his epic poem Childe Harold's Pilgrimage. Scientists analyzed samples of the ancient concrete used to build the tomb, describing their findings in a paper published in October in the Journal of the American Ceramic Society.
The monument and landmark on the Via Appia Antica indicates that Caecilia Metella was held in high regard, according to co-author Marie Jackson.
Portland cement is a basic ingredient of modern concrete, like ancient Roman concrete was a mix of semi-liquid mortar and aggregate. Portland cement is usually made by heating limestone and clay in a kiln. The aggregate used to make Roman concrete was made up of fist-size pieces of stone or bricks.
The Roman architect and engineer Vitruvius wrote about how to build concrete walls for funerary structures that could last a long time without falling into ruins. The walls should be at least two feet thick, made of either "squared red stone or of brick or lava laid in courses." The brick or volcanic rock aggregate should be bound with mortar comprised of hydrated lime and porous fragments of glass and crystals from volcanic eruptions.
Portus Cosanus pier is in Orbetello, Italy. A study found that the formation of crystals in the concrete helped prevent cracks from forming.
Jackson has been studying Roman concrete for a long time. She and several colleagues analyzed the mortar used in the concrete that makes up the Markets of Trajan, which is believed to be the world's oldest shopping mall. They were interested in the glue that was used in the binding phase, which was augmented with crystals of stratlingite. They found that the formation of microcracks in the mortar could have been prevented by the blocking of the crystals.
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Jackson co-authored a paper analyzing the ruins of sea walls along Italy's Mediterranean coast, which have stood for two millennia despite the harsh marine environment. The Roman sea walls seem to have gotten stronger despite the constant salt-water waves crashing against them.
Jackson and her colleagues found that the secret to longevity was a combination of rare crystals and a porous mineral. Exposure to sea water caused chemical reactions inside the concrete, which resulted in the formation of aluminum tobermorite crystals, a common mineral found in volcanic ash. The formation and propagation of cracks that would have weakened the structures were prevented by the crystals bound to the rocks.
The Tomb of Caecilia Metella is one of the best-preserved monuments on the Appian Way. Jackson visited the tomb in June of 2006 and took samples of the mortar for analysis. She remembered that the air inside the sepulchral corridor was very cool and moist after she left. Jackson said the atmosphere was tranquil, except for the fluttering of pigeons in the open center.
A plaque on the tomb reads "To Caecilia Metella, daughter of Quintus Creticus and wife of Crassus".
Caecilia Metella, the noblewoman whose remains were once interred in the tomb, was the daughter of a Roman consul, and so little is known about her. She married Marcus Licinius Crassus, whose father was part of the First Triumvirate. It was likely that her son ordered the construction of the mausoleum, so historians can keep track of the family genealogy.
The marble sarcophagus housed in Palazzo Farnese is said to be from the Tomb of Caecilia Metella, but it is probably not the noblewoman's since it dates to between 180 and 190CE.
Jackson and her colleagues are interested in the structure of the tomb. The mausoleum is on top of a hill. The attached castle was built in the 14th century and is located at the rear of the rotunda. There is a plaque on the exterior of the building.
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The substructure of the tomb has lava in it.
The foundation is built on lava rock from an ancient flow that once covered the area. The podium and rotunda are made of several layers of thick concrete, surrounded by travertine blocks as a frame, while the concrete layers formed and hardened. The tower walls are thick. Medieval battlements replaced the conical mound that would have been on top.
Jackson, Linda Seymour, Admir Masic, and Lawrence Berkeley Lab's Nobumichi Tamura collaborated to take a closer look at the tomb mortar's microstructure. Tamura was able to identify the many different minerals contained in the samples by analyzing them at the Advanced Light Source. The x-ray beams produced by the beam line can penetrate through the entire thickness of the samples. The samples were imaged with scanning electron microscopy.
They found that the tomb's mortar was similar to the one used in the Markets of Trajan. The tephra used in the tomb's mortar contained more leucite. The tomb's walls were seeped through over the centuries, which dissolved the leucite and released the potassium. This would cause a disaster in modern concrete, producing micro-cracking and serious damage to the structure.
That didn't happen with the tomb. But why? The C-A-S-H binding phase was changed by the dissolution of the potassium in the mortar. Some parts remained intact even after 2000 years, while other areas looked more like they had split. The structure was similar to that of nanocrystals.
The image is a scanned electron microscope image.
The interfacial zones in the ancient Roman concrete of the tomb of Caecilia Metella are constantly evolving through long-term remodeling. The remodeling processes could contribute to improved mechanical performance and resistance to failure of the ancient material.
The closer we get to being able to reproduce the qualities of Roman concrete, the more likely we are to find a substitute for volcanic rock. It could improve the lifespan of modern concrete structures by as much as 85% and reduce the energy emission of producing concrete by as much as 85%.
Masic said, "Focusing on designing modern concretes with constantly reinforcing interfacial zones might provide us with yet another strategy to improve the durability of modern construction materials." The integration of time-proven Roman wisdom could improve the longevity of our modern solutions by orders of magnitude.
The journal of the American Ceramic Society was published in 2021. The About DOIs page has more information.
