2,200-Year-Old Roman Shipwreck Reveals Ancient Waterproofing Secrets

For as long as people have traveled by sea, ships have needed protection from water, salt, microorganisms and marine worms. Yet until the mid-20th century, researchers paid relatively little attention to the non-wood materials used in ancient shipbuilding. A new study published in Frontiers in Materials analyzed the protective coating on the Roman Republic shipwreck Ilovik-Paržine 1, which sank about 2,200 years ago off the coast of what is now Croatia.

"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 first author Dr. Armelle Charrié, an archaeometrist at the Laboratory of Mass Spectrometry of Interactions and Systems in Strasbourg. The study found two different coatings on the vessel: one made of pine tar, also called pitch, and the other a mixture of pine tar and beeswax. Analysis of pollen trapped in the coating helped identify the plant species present in the environment during the ship's construction or repairs.

The researchers used methods including mass spectrometry to analyze 10 coating samples. Molecular fingerprinting showed every sample was dominated by heated coniferous resin or tar. One sample, however, contained a different formulation of beeswax and tar — known to Greek shipbuilders as zopissa — which improves adhesive flexibility and is easier to apply while hot.

Because pitch is naturally sticky, it can capture pollen from nearby vegetation. Studying the pollen types recovered from the coatings pointed to a wide range of environments: forests of holly oak and pine typical of Mediterranean and Adriatic coasts, olive- and hazel-growing shrubland known as matorral, alder and ash pollen from riverbanks and seashores, and small amounts of fir and beech associated with the mountainous terrain of Istria and Dalmatia.

The analysis suggests the vessel received four to five separate batches of coating over time. Earlier research on the ship's ballast had pointed to Brundisium — today Brindisi, on Italy's south-eastern coast — as the place where the ship was built. The new pollen evidence suggests some of its coatings may also have been applied there, while others were added along the north-eastern Adriatic coast, close to where the wreck was found.