Dolium - Dolia in Maritime Commerce - Construction of Dolia Ships

Construction of Dolia Ships

The “La Giraglia” shipwreck, discovered off the coast of Corsica, France, is particularly interesting because it is officially recognized as a cistern boat. This type of vessel was intended to transport dolia in bulk as the dolia appear to have been placed in the hold as the ship was being built. The “La Giraglia” was carrying at least eight dolia and its excavation gives insight into the ship’s design and how such vessels contributed to patterns of trade in the western Mediterranean. The cistern boat was an innovation in ship construction, intended to respond to changes in the production and transportation of wine brought about by Roman expansion. The cistern boat began being built during the Augustan Period, and continued until the 2nd century. The relatively short period of production for this ship-type suggests that there were problems with its design which caused the design to be superseded. Because each discovery illuminates the ways in which maritime commerce adapted to the demands of production and transportation, the “La Giraglia” shipwreck is essential in the understanding of mutual exchange within the Mediterranean.

As this dolia ship came to a very traumatic ending, there is little left to be excavated and studied of the hull. The hull planking is also poorly preserved, but there were, however, thirteen strakes that may serve for extrapolation to the design of the entire ship. The strakes were fastened together by pegged mortise and tenon joinery and assembled in the classic shell-first construction. The spacing between mortises and the width of the mortises is very tight and they also appear to be slightly wider than the tenons. It is believed that the space left within the mortises was intended to compensate for possible misalignment of opposite mortises. It appears that they were arranged in a straight line, rather than alternating from the inboard to the outboard edge and the back inboard in order to prevent the wood from splitting. Twenty-six frames were also identified and recorded from the “La Giraglia” dolia shipwreck. The large quantity of nails indicates their significance as a strengthening element in the assemblage of the frames with the planking.

The “La Giraglia” was a medium sized ship, but possessed a few rather unusual characteristics because the discovery and study of the twenty-six frames reveal that 58.8% of the preserved hull was composed of oak. The use of oak solely for the hull planking has never before been seen in the Mediterranean. However, given the fragmented nature of the remaining wreck, this preponderance of oak in the surviving portions may not reflect the composition of the rest of the original ship. It could have perhaps only been used for the bottom of the hull, which would certainly be an interesting characteristic for such cistern boats. The ship builder might have thought it necessary to use this hardwood because the weight of the cargo was concentrated in the center section of the ship. Overall, there were six species of wood used in the construction of the “La Giraglia”: oak was used for the frames and tenons, beech and elm also for the frames, ash made up the small pegs used in the hull planking, and fir and two other types of oak. The shipwright obviously knew how to use the available species appropriately for the construction of the different structures and elements of the ship.

“Whatever the answers to the numerous questions raised about the dolia vessels or cistern boats, these ships must be considered not only as a technical innovation of their time, but also as a daring enterprise. The presence of huge containers in the hold presented an obvious and real danger. The rupture of a full dolium would have caused almost two tons of wine to pour rapidly into the hold, which could have resulted in a sudden destabilization and capsizing of the vessel. In spite of the advantages of dolia over amphoras, the obvious risks may explain why cistern boats disappeared”.