The ship’s critical waterproofing layer was their treasure. This unique protective layer on a ship traps pollen in its stickiness just like tree sap. By studying the type and quantity of pollen, as well as the molecular composition of the coating itself, researchers can start forming theories about where the boat was when this essential coating was created and applied.

“In archaeology little attention is paid to organic waterproofing materials. Yet they are essential for navigation at sea or on rivers and are true witnesses of past naval technologies,” Armelle Charrié-Duhaut, first author of the paper and an archaeometrist from the University of Strasbourg in France, said in a statement. As such, Charrié-Duhaut and her colleagues employed structural, molecular, and pollen analyses to investigate 10 coating samples from Ilovik–Paržine 1.

The waterproofing layer’s “molecular fingerprint” thus came to light, revealing that either heated coniferous tree resin or heated coniferous tar (also called pitch) was the main ingredient in all their samples. However, according to one sample, some unknown quantity of the coating consisted of a mixture of beeswax and tar that Greek shipbuilders called zopissa. “The use of pitch and beeswax by the Greeks is mentioned in Pliny the Elder’s Natural History (XVI, 23),” Charrié-Duhaut tells Popular Science.

“The identification of this mixture on the Ilovik-Paržine 1 shipwreck attests to the continued use of this type of composition in an Adriatic context.” The use of zopissa on an ancient Roman ship also supports the hypothesis that the vessel was built in Brundisium. Now the present-day Italian city of Brindisi, the region was in contact with mainland Italy’s Greek colonies at the time. The pollen analysis aligns with this theory as well, indicating that part of the coatings were put on the ship in proximity to that area.

The ship may have received others somewhere on the northeastern Adriatic coast—where it met its final doom. More broadly, the pollen came from a diverse group of environments, including forests of holly oak and pine,shrublands with olive and hazel trees, areas with alder and ash trees, and regions with fir and beech trees. Some of these plants are typical of Mediterranean and Adriatic coasts and valleys.

As for the protective layers themselves, the vessel probably received four to five different rounds of coatings. The same layer was applied on the stern and central part of the ship, but the bow had three separate batches of application, which may suggest consecutive patch-up jobs using materials from across the Mediterranean. “Our study highlights navigation routes based on clues related to the ship’s construction areas and, especially, to the different phases of coating application on the ship.

It suggests that this vessel traveled between the western Adriatic coast, where it was likely built and where the first layer of coating was applied, and the eastern Adriatic coast,” says Charrié-Duhaut. “Movements between the southern and northern sections of this eastern coastline are also possible, where repairs or recoating could have been carried out during the ship’s lifetime.”