Here’s what you’ll learn when you read this story:

• A Roman Republic-era shipwreck found off the coast of Croatia highlights the importance of waterproofing in the second century B.C.E.
• Analyzing the adhesive coating using a mix of scientific methods created a clearer picture of the ship’s movements.
• Historic mixtures of resin and beeswax were present in a layer of the ship’s waterproofing.

For most people, pollen is just an irritating allergen. But archaeologists recently used centuries-old specks of the stuff found within the waterproofing pitch on an ancient Roman ship to uncover the vessel’s journey through history, one that likely started in Italy and ended with its demise in Parzine Bay off Ilovik Island, Croatia.

The second-century B.C.E. Roman ship, which was dubbed Ilovik-Parzine 1 following the discovery of its wreckage off the Croatian coast in 2016, is the subject of a new study published in the journal Frontiers in Materials. The research provides intricate analyses of the waterproofing coatings on the timber, combining chemical analysis with pollen study to see how adhesive technologies have changed, as well as the history of where this ship once voyaged.

The study’s findings ended up mapping out quite the route for the ship, which was likely constructed in Italy before sailing throughout the Adriatic Sea until it sank roughly 2,200 years ago near Croatia. The authors wrote that much research has been focused on understanding ancient ship design and timber origin, but investigating something else common to every ship, waterproof coatings, has gone largely untouched.

Over time, resins, bitumen, plant tars—pure or mixed with beeswax—fats, and inorganic elements have all been used as waterproofing to help seal the crevices in the wood foundation of ships, offering a layer of protection against corrosion, worms, and pests. The expansion of shipbuilding between the 13th and 19th centuries led to the growth of an entire industry for processing plant tars, but the history of such concoctions goes much deeper, with ancient Roman author Pliny the Elder discussing the use of a mixture of pitch and beeswax called zopissa that has been found by modern archaeologists in sites as old as the seventh century B.C.E.

The Ilovik-Parzine 1 borrows some of this same technology.

The study found that the Ilovik-Parzine 1 featured at least four different coating applications in varying layers, and while chemical analysis showed they were all relatively similar, further investigations spotlighted differences. Across the 10 samples taken, most of the waterproofing adhesive featured intensely heated conifer resin (likely pine), showing clear technical know-how by the ancient craftspeople. But one sample was different, a zopissa blend that included beeswax, which made the resin easier to apply.

It was the pollen testing that really opened further avenues of exploration. Pollen trapped within the sticky resin helped the authors map where the coating was either produced or applied. They found traces of Mediterranean shrublands filled with olive and hazel, forests of holly oak and pine, coastal alder and ash, and even upland fir and beech. The unique blends showed that the ship was likely built near present-day Brindisi in southern Italy, a key Roman-era port, and then repaired as it moved across the Adriatic.

“These coatings bear witness to the ship’s life over time and to its movements on the sea,” Arnelle Charrie, corresponding author, told Discover. “It highlights common patterns and regional specificities, notably in relation to the availability of natural resources.”

With no historical records of Roman ship maintenance, Charrie said turning to chemical analysis combined with the study of pollen helped the team to distinguish between batches of adhesives. “They are part of the heritage materials, and their study [is] potentially rich in information,” she said. “They tell a story….Chemically, on this wreck, the surprise was the discovery of a sample composed of pitch and beeswax, in contrast to the majority of samples which consisted solely of pitch.” She added that this example “illustrates the circulation of technical knowledge and the phenomena of technological transfer across the Mediterranean basin.”

Despite the merchant vessel sailing the seas in 170 B.C.E., the Ilovik-Parzine 1 has found a new purpose. “This analytical strategy,” the authors of the study wrote, “opens new fields of investigation in naval archaeology.”