As it is used in line 81, the word free most nearly means: 31 GO ON TO THE NEXT PAGE. ACT-G20 3 3 85 90 www.actexam.net www.crackab.com Passage II SOCIAL SCIENCE: This passage is from the article “Built to Last” by Nikhil Swaminathan. The Romans started building with concrete regu- larly beginning in the third century B.C., but the earliest uses go back roughly a thousand years further, to ancient Greece. Concrete is made of chunks of rubble held together by mortar. Today, mortar is typically made by mixing gravel, sand, and binders such as lime and cement. According to Marie Jackson, a research engineer at the University of California, Berkeley, and ROMACONS (Roman Maritime Concrete Study) col- laborator, modern concrete begins to break apart under- water. The material used by the Romans for maritime construction, however, actually gets stronger over time. In the first century B.C., the architect and engineer Vitruvius wrote an expansive work on Roman building methods called De Architectura. In it, he describes a substance found near Baia, a resort town on the Bay of Naples, and around Mount Vesuvius, that “when mixed with lime and rubble, not only lends strength to build- ings of other kinds, but even when piers of it are con- structed in the sea, they set hard under water.” The ROMACONS team set out to confirm what Vitruvius had written by studying the concrete used to build harbors dotting the Mediterranean, including Caesarea, Portus (one of Rome’s great harbors), Pompeiopolis in modern-day Turkey, and Hersonissos in northern Crete. The researchers took cores, measur- ing four inches in diameter and up to 20 feet long, from various parts of each harbor, many of which are now submerged. Jackson was then enlisted to investigate the con- crete’s physical characteristics and material makeup. She found that its compressive strength, meaning the weight it can bear, was much lower than that of modern concrete, so it wasn’t suitable for tall aboveground architecture. When she compared the trace elemental composition of the mortars in the cores, however, she confirmed Vitruvius’ assertion. All the samples con- tained volcanic ash that came either from Mount Vesuvius or Campi Flegrei, volcanoes located east and west of Naples, respectively. The same ash was also found in a sample sent to the team from Quarteira on the coast of southern Portugal. The specific type of ash is known as pozzolana after Pozzuoli, the town near Campi Flegrei where it was originally used, but John Oleson, a classical archaeologist at the University of Victoria in British Columbia, says you can find it throughout the Bay of Naples. “If you’re rowing a boat along the coast near Baia, parts of the coastline are made up of this poz- zolana,” he explains. Jackson credits the Romans with noticing that, over time, the ash consolidated into a volcanic rock called tuff. With that insight they formulated their unique mortar recipe: pozzolana, lime, and seawater. That mixture, which she says must have been arrived at by careful experimentation, results in the growth of a durable binding substance throughout the concrete mix- ture. “Pliny the Elder says that they needed something that lasts a long time and gets stronger with age,” Jackson explains, quoting the ancient Roman scholar and natural historian. Because seawater is part of the reaction, placing this mortar in the Mediterranean pro- motes greater adhesion rather than causing the concrete to crack. According to Oleson, the Romans relied on the pozzolana for maritime construction for two centuries, beginning about 40 B.C. He suggests that its presence in ports as far east as Caesarea and Alexandria shows that the ash was exported throughout the empire from the Bay of Naples. “ROMACONS has managed to document the evo- lution of this [maritime concrete] industry and the type of materials used, and to document the trade across the Mediterranean, a trade that previously was not known,” Oleson explains. He posits that, for example, a grain ship arriving in Rome’s Portus from Alexandria might have been sent back with pozzolana stored in sacks for ballast, which would then be used in port construction back east. The reactivity of Bay of Naples pozzolana was well known in antiquity, says Lynne Lancaster, a clas- sics professor at Ohio University. She has documented shorter-range trade within the Roman Empire in her research, including the export of lightweight volcanic rocks from Sardinia for use in building vaults in Carthage. What the ROMACONS project has identified, Lancaster says, “is a Mediterranean-wide trade that is being used to build the ports, which in turn is used to increase the trade. This contributes more to the eco- nomics and infrastructure of the Roman Empire.” From the article “Built to Last” by Nikhil Swaminathan (©2014 by Archaeology Magazine). Used with permission.
