The route of a Roman ship has been able to be reconstructed thanks to pollen

BarcelonaWe know many things about the Romans, because they left extensive documentation that mainly recounts their exploits, the intrigues of emperors, and the daily lives of ordinary mortals. A vast amount of archaeological evidence, both on land and at sea, has also uncovered everything they built and the technical advances they achieved. With bioarchaeology, it is even possible to know with precision what materials they used to make vessels as waterproof as possible and where they built and repaired them. And to delve into very specific details like those revealed by a new study published in Frontiers in Materials, with researchers from France and Croatia, which analyzes the coating of a Roman vessel (called Ilovik–Parzine 1), which sank approximately 2,200 years ago off the coast of what is now Croatia.

The Romans developed a technology that allowed them to follow the great maritime routes that the Phoenicians and Greeks had already initiated for trade throughout the Mediterranean. They were capable of building maritime infrastructure almost anywhere: not only did they serve as anchorages in natural harbors, but they also erected breakwaters, quays, and jetties directly in the sea, creating artificial bays protected from the waves. This allowed them to navigate with larger ships with deeper drafts and greater cargo capacity, and to circulate wine, grain, oil, and many other goods through a network that connected ports, warehouses, and roads. But to supply the large cities with products arriving from all corners of the Roman Empire, they also needed vessels that were waterproof, resistant to saltwater, and capable of repelling marine microorganisms, such as wood-boring worms.

The technique to achieve this is not theirs. Since the first vessels made from hollowed-out logs, it has been a challenge to make them so waterproof. Various ancient sources document the use of natural adhesive substances, such as the account in the

Epic of Gilgamesh, which describes the use of bitumen to seal vessels. The Greeks already mixed tar with beeswax, a technique that shipbuilders called zopissa.

The novelty of a new study published in Frontiers in Materials is that it has been able to follow the trace left by pollen stuck to the resin of the vessel. The analysis of the wreck confirms that the ship was built in the 2nd century BC using the mortise and tenon technique, which precisely fitted the different timbers together, which were then reinforced with dowels.

"In archaeology, little attention is paid to organic waterproofing materials. However, they are essential for maritime or river navigation and are true testimonies of past naval technologies," explains Armelle Charrié-Duhaut, archaeometrist at the Laboratory of Mass Spectrometry of Interactions and Systems in Strasbourg. According to the researcher, the study of the coatings has made it possible to identify two types of materials on the ship: one made of pine tar and another of a mixture of pine tar and beeswax. The analysis of the pollen present in these coatings has made it possible to identify the plant taxa of the immediate environment during the construction or repairs of the ship. In other words, by following the pollen trail, it is possible to know where it was built and in which ports it was repaired. "The study of the itinerary is what is called a pollen fingerprint," explains Santiago Riera, professor of history and archaeology at the University of Barcelona. "When resin is applied to a ship, it is done when hot, and that is why the pollen sticks; when the adhesive cools, it gets trapped inside and, therefore, the risk of contamination is practically non-existent," adds Riera.

All the clues that pollen gives

"This research demonstrates that naval adhesives are not merely technical materials, but also indirect indicators of mobility, exchange, and knowledge circulation in the Roman Mediterranean, reflecting the complexity of the naval and commercial networks of the time," state the study's authors. Specifically, researchers from the underwater archaeology department of the Croatian Conservation Institute and the ADRIBOATS program at the Camille Jullian Center of Aix-Marseille University have analyzed ten coating samples from different parts of the vessel. With the results, they have delineated the possible regions where the material was produced and applied during maintenance tasks. The integration of palynological and geoarchaeological data suggests that a significant portion of the coatings could have been produced or applied in the Brundisium area (modern Brindisi, in southeastern Italy), while other layers might correspond to repairs in different ports during the vessel's lifetime.

In the laboratories, they found a great diversity of plant environments: Mediterranean forests of holm oak, pine, and cistus, scrubland with olive trees and other Mediterranean shrubs, as well as humid areas with alder, ash, and sedges typical of areas near rivers and coasts. To a lesser extent, fir and beech, typical of mountainous regions of the northeastern Adriatic, such as the Istrian and Dalmatian mountain ranges, were also detected.

"Although it seems evident that vessels traveling long distances need repairs, it is not always easy to prove it. Pollen has been very useful in distinguishing different coatings when molecular profiles were practically identical," concludes Charrié-Duhaut. The wreck was discovered in 2016 and has since been the subject of various study campaigns. This work is the first to combine molecular and palynological analyses to study the coatings in detail and reconstruct the environments associated with their production and use.

"We also carried out a study of the Barceloneta I and were able to confirm that the pitch used for its construction came from Atlantic forests and that the ship was later repaired in a Mediterranean port – explains Riera–. The study of Ilovik-Parzine 1, however, provides a much higher resolution analysis and can specify much more precisely where the repairs were made." One of the objectives of the professor at the University of Barcelona is to apply a similar study to what is now being published in Frontiers in Materials to the wreck found in April 2025 in Ciutadella.