The secrets of waterproofing ancient Roman ships to withstand long and harsh sea voyages have now been revealed, after archaeologists investigated a 2,200-year-old shipwreck off the coast of modern-day Croatia.
Seafaring in the ancient world was no easy task, as keeping water out was not the only concern: corrosive salts, microorganisms, and worms also represented small—but significant—threats to the seaworthiness of Roman sailing vessels over time.
Now, a collaboration between French and Croatian researchers reveals how the ancient Romans solved these challenges, as detailed in a new study published in Frontiers in Materials.
Roman Water-Proofing Techniques
Only in the mid-20th century did archaeologists turn their attention to how the ancient Romans preserved their ships as they voyaged the seas, and even then, only a small cohort investigated the matter, leaving many questions unresolved. Now, as researchers uncover evidence from the shipwreck Ilovik–Paržine 1, pieces are coming together on how protective coatings were applied to organic materials in the Roman Republic.
“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,” said lead author Dr. Armelle Charrié, an archaeometrist at the Laboratory of Mass Spectrometry of Interactions and Systems in Strasbourg.
“Studying the coatings, we found two different kinds on this vessel: one made of pine tar, also called pitch, and the other of a mixture of pine tar and beeswax,” Dr. Charrié adds. “Analysis of pollen in the coating made it possible to identify the plant taxa present in the immediate environment during the construction or repairs of the ship.”
Exploring a Roman Shipwreck
It’s been a decade since the shipwreck was first discovered, with multiple explorations of the cargo and structure over the last ten years; however, none had previously examined the composition of the wreck’s coating in such depth. The French and Croatian teams used pollen and molecular analysis, including mass spectrometry, to study the coating applied to the ship during production and after. This allowed them to conclusively identify the components and their amounts in the mixture.
“Some regions throughout the Adriatic have particular characteristics that led local populations to develop a specific shipbuilding style,” said Charrié. “Only studies like ours offer an overview into these traditions which bear witness to genuine know-how and diverse traditions.”
Ten samples were collected for analysis, with one showing a quite different composition from the others. All samples indicated that heated coniferous pitch or pine resin, also known as pitch, served as the basis for the substance. Yet one sample appeared to be of a Greek ship coating called zopissa, a combination of pitch and beeswax, noted for its flexibility and ease of application when heated.
Tracking Ancient Roman Sea Journeys
Earlier research identified Brindisi, then known as Brindisium, as the site of ship construction, yet not its history of travel.
Intriguingly, the samples contained clues to where the ship was constructed or repaired over its lifetime, offering new indications of its travels. This is a side effect of pitch’s adhesive nature, which captures and preserves pollen floating in the air as it is applied and sets.
Pollen recovered from the wreck came from a wide variety of locations across the Mediterranean and the Adriatic. Specifically noted by the team were pollens common to holly oak and pine forests, as well as scrublands full of olive and hazel. Coastal environments were represented by alder and ash, accompanied by a smaller amount of fir and beech.
In their analysis, the researchers identified 4 to 5 distinct batches of the coating, indicating that continuous repair work was carried out on the ship, targeting specific areas.
“While it seems obvious that ships sailing long distances need repairs, it’s simply not easy to demonstrate this,” concluded Charrié. “Pollen has been very useful in identifying different coatings where the molecular profiles were identical.”
The paper, “Adhesive Coatings in Naval Archaeology: Molecular and Palynological Investigations on Materials from the Roman Republican Wreck Ilovik– Paržine 1 (Croatia),” appeared in Frontiers in Materials on April 24, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.