April 5, 2013
Ancient Battering Ram Analysis Reveals Details Of Its Origin
Lawrence LeBlond for redOrbit.com - Your Universe Online
A bronze battering ram from a 2,000-year-old warship discovered by British divers off the coast of Libya in 1964, is offering up some evidence for how such a device was made in ancient times. Analysis of the 45-lb, 26-inch-long artifact, which is known as the Belgammel Ram, revealed that the process used to build the weapon was not easy.
The ram comes from a small Greek or Roman warship (tesseraria), which was equipped with massive bronze rams on the bow at the waterline used for ramming the sides of enemy ships. The Belgammel Ram would have been found on the upper level on the bow. A second ram, known as a proembolion, would have supported the bow and had been used to break oars on an enemy ship.
Dr. Nic Flemming, a marine archaeologist from the National Oceanography Centre (NOC), coordinated a team of specialists from five institutions to analyze the ram before it was returned to the National Museum of Tripoli in 2010. The results of their analysis have been published in the International Journal of Nautical Archaeology.
“Casting a large alloy object weighing more than [44 pounds] is not easy. To find out how it was done we needed specialists who could analyze the mix of metals in the alloys; experts who could study the internal crystal structure and the distribution of gas bubbles; and scholars who could examine the classical literature and other known examples of bronze castings,” said Flemming in a statement.
“Although the Belgammel Ram was probably the first one ever found, other rams have since been found off the coast of Israel and off western Sicily. We have built a body of expertise and techniques that will help with future studies of these objects and improve the accuracy of past analysis,” he added.
Radiocarbon dating of the burnt wood found inside the ram dates it to between 100 BC and 100 AD, which is consistent with the decorative style of the tridents and bird motif on top of the ram. Dr. Chris Hunt and Annita Antoniadou of Queen´s University Belfast provided the radiocarbon dating and Dr. Jon Adams of the University of Southampton provided laser scanning that discovered the tridents and bird motif.
The team believe that during its early history the bronze would have been re-melted and mixed with other bronze on multiple occasions, perhaps during repair of the warship.
Dr. Richard Boardman of m-VIS, a dedicated center for computed tomography (CT) at Southampton, helped produce a 3-dimensional image of the ram´s internal structure using a machine capable of generating X-rays strong enough to shine through 6 inches of solid bronze. By rotating the ram on a turntable and making 360 images they created a complete 3D replica of the ram.
Analysis of the structure was also carried out by Professor Ian Croudace, Dr. Rex Taylor and Dr. Richard Pearce, geochemists at Southampton´s Ocean and Earth Science. Micro-drilled samples show that the composition of the bronze was 87 percent copper, 6 percent tin and 7 percent lead.
Further analysis showed that the concentrations were different throughout the casting. Scanning Electron Microscopy (SEM) revealed that the lead was not dissolved with other metals to make a composite alloy, but had separated out in blobs within the alloy as the metal cooled.
Analysis indicates that the ram was likely cast in one piece and cooled as a single object. The thicker parts cooled more slowly than the thin regions so the crystal structure and number of bubbles trapped in the metal varies.
Through isotopic analysis of the metals, researchers are able to pinpoint the origin of the lead ore used in making the metal alloy. Previous analysis could only provide a generalized location in the Mediterranean. But new developments in the analysis technique means the team can make an ever more accurate estimate of where the lead ore derived.
Their updated analysis shows that the ore could have come from a district of Attica in Greece called Lavrion. With this new advance, the team believes they can pinpoint origins of the ores of other ancient metal artifacts with high accuracy.
The Belgammel Ram was discovered by a group of three British service sports divers off the coast of Libya at the mouth of the Waddi Belgammel valley, near Tobruk. The divers used a rubber dinghy and rope to pull the artifact 82 feet to the surface. The divers took the ram back to the UK as a souvenir but later loaned it out to the Fitzwilliam Museum in Cambridge once they learned the artifact was a rare antiquity.
In 2007, the sole surviving member of that dive team, Ken Oliver, decided the ram should be returned to a museum in Libya. Arrangements were made and the ram was returned home to Libya in 2010. For the time before the return, Flemming and colleagues studied and analyzed the ram extensively.
“We have learned such a huge amount from the Belgammel Ram and have developed new techniques which will help us unpick future mysteries,” said Flemming.
“We will never know why the Belgammel Ram was on the seabed near Tobruk. There may have been a battle in the area, a skirmish with pirates. It could be that it was cargo from an ancient commercial vessel, about to be sold as salvage,” he continued.
“The fragments of wood inside the ram show signs of fire, and we now know that parts of the bronze had been heated to a high temperature since it was cast which caused the crystal structure to change. The ship may have caught fire and the ram fell into the sea as the flames licked towards it. Some things will always remain a mystery. But we are pleased that we have gleaned so many details from this study that will help future work,” Flemming concluded.