This past May, Concrete Construction was offered the opportunity to take a step a back in time -- approximately 2000 years -- to examine construction materials and methods uncovered at an excavation site in Egypt. Visiting the excavation site required a trip halfway around the world to Alexandria, Egypt, located approximately three hours north of Cairo. Even more intriguing, the excavation site is located underwater in a harbor just off Alexandria.
Leading the international excavation team is French underwater archeologist Franck Goddio who has spent close to 10 years on the site. Since 1992, Goddio has uncovered Cleopatra's royal palace as well as two ancient cities buried beneath the Mediterranean Sea for almost 1600 years after a series of tidal waves and earthquakes. Topographical surveys have assisted Goddio's team, which is sponsored by the Hilti Foundation, overcome the poor visibility in the harbor's water to excavate the ancient ruins located on the harbor floor. Many items discovered by Goddio's team include coins, granite statues, pottery, granite structures, and limestone blocks. Of even more importance, tools and materials, such as mortar, have been uncovered revealing clues as to how the ancient cities were constructed.
Many of the construction materials and methods, including quality of construction, were just as important 2000 years ago as they are today. CC sat down with Egyptologist David Fabre, a member of Goddio's team, to discuss the ancient construction materials and methods.
CC: Are there specific materials, such as cement and concrete, that were used in these early cities? If so, has any research and/or testing been done into the makeup of these materials?
DF: The vast majority of the construction in ancient Egypt was in mud brick, which appeared during the predynastic period. Some very important buildings, such as temples and pyramids were made of stone. Some of the other construction materials used since the origins of Egypt included wood, reed, and mud. Brick was employed next, and used often during the Middle or the New Kingdom, and more so since the 26th dynasty. However, its use is more current since the Roman time, and used primarily for the construction of entire buildings. Brick was not used prior to these times because it was expensive and took a long time to produce. Additionally, mortar made of soil was used for building mud-brick walls between the different layers of brick.
CC: What type of construction tools were used in the ancient cities? Is there evidence of these tools and methods in today's construction industry?
DF: Certainly, there is evidence of these tools today. In the ancient cities, the construction tools were very simple, and made of stone, copper, or bronze. These types of tools include chisels, mallets, and pick-hammers. Larger tools were manufactured to carry bricks, blocks, and statues. For the architect, tools included levels and different types of vertical gauges for measuring plumb lines. Other measuring instruments included rules, ropes, and squares.As far as construction methods, Egyptians used mud-brick for a very long time for building houses. But now, the use of mud-brick is forbidden by the government, to avoid the waste of agricultural soil. However, today you can still see in the Delta, for example, smaller cowsheds made of adobe.
CC: Is there evidence of concrete or objects containing concrete at the excavation site?
DF: Yes, for example, the port structures identified to the east of the Portus Magnus of Alexandria feature foundations made of large blocks of mortar and limestone debris contained in a formwork of piles and planks. The piles are square with notches on both sides to accommodate the pile planks.
Analysis has shown that care was taken in choosing mortar ingredients, which were natural and included quartz, sand, and various rock fragments. Also, anthropic ingredients included plant fragments, charcoal debris, ceramic debris, and the byproducts of lime calcination.
The diameters also are quite varied from several tenths of a millimeter to 2 cm. Yet, great care was taken in producing and mixing the mortar to ensure an even consistency, which explains its strength. Additionally, it must be noted that the broken tile mortar technique, a highly water-resistant mixture of lime and pozollans (volcanic ash or ground ceramic dust) used frequently by the Romans from the 1st century BC and onward, was not present in the Alexandria excavation.
Wood samples have been taken in two places for analysis. Close to the shore, the oak piles date from 220 AD, and the pine planks from 155 AD. At the end of the dock, the oak piles date from 115 AD, and the pine planks from 70 AD. Pieces of paving, especially limestone slabs, have been identified in a section south of the mortar block arrangement. These originally would have been positioned on the mortar.
CC: How did the excavation site come to rest in its current position in the Mediterranean?
DF: The results of the work show the sites were subject to geological and cataclysmic phenomena over various periods confirming the slow movement of land subsidence affecting this section of the southeastern basin of the Mediterranean. These factors, independently or together, may have caused considerable destruction and explain the underwater disappearance of the Portus Magnus and a large part of the region. All evidence has shown that regular subsidence and the rising sea level - observed since ancient times - contributed to the submergence of the land area in question. This generally acknowledges the sea level in Alexandria has risen by 1 to 1 1/2 meters and the land level dropped by 5 to 6 meters over the last 2000 years.
The southern coast of the eastern Mediterranean also has been subject to various forms of tectonic movement due to the subduction of the African plate under the Anatolian plate. Ancient texts give accounts of earthquakes and tsunamis affecting the region, especially the tsunami of July 21, 365, which affected the southeastern Mediterranean coasts as well as an earthquake in the mid-8th century.
Although topographical maps correspond to indications provided by ancient authors, they also offer an accurate representation of the actual situation in the field. The presence or absence of a trench line has determined which rocky ledges created outcrops and which emerged in ancient times. The ruins of vast buildup areas have been found. These were preserved by their submersion from being covered and broken up, as has happened to other areas of the ancient city from medieval times through the present.
We are still a long way from being able to date the development and transformations of each sector, assign or name the structures which may have existed, or determine the date or circumstances which reduced the site to chaotic ruins.By analyzing the configuration and the composition of the site, and the anthropic and geological substrata of the areas still accessible to marine exploration, it is possible to determine step by step the extent to which buildings were leveled, the area of subsidence, signs of reuse, sawing or technical rework, intentional destruction following the desecration of pagan temples, attempts to protect the coast from potential tsunamis, or to alleviate the results of subsidence.
Artifacts on display:
Findings from the expeditions of Goddio and his team off the coast of Egypt are on display at the Franklin Institute in Philadelphia until January 2011. The exhibition "Cleopatra - The Search for the Last Queen of Egypt" will be shown in five North American cities. It is organized by National Geographic and Arts & Exhibitions International, with cooperation from the Egyptian Supreme Council of Antiquities and the IEASM. For information, visit The Franklin Institute or NationalGeographic.com.