Roman-Era Wreck Reveals How Ships Were Built to Last 2,000 Years Ago

During the mighty reign of the Roman Empire, thousands of years ago, technology was built to last.

From a ship that sank in the Adriatic Sea some 2,200 years ago, archaeologists are discovering the techniques Roman-era shipbuilders used to keep their vessels seaworthy for years after construction.

The ancient wood reveals not only that the ship was cleverly waterproofed with pitch, but that it underwent renewed coating at different ports over the course of its life.

"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," says archaeometrist Armelle Charrié-Duhaut of the University of Strasbourg in France.

"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. 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."

The wreck, named Ilovik-Paržine 1, was discovered in 2016 off the coast of what is now Croatia, under just 4 meters (13 feet) of water. Like many ancient shipwrecks, it had broken apart and been buried under rocks and sediment, blending into the seafloor and evading notice.

That burial is what preserved it. The normal processes of decay, facilitated by organisms such as microbes and shipworms, require oxygen. Burial under the seafloor limits the oxygen supply, preserving at least part of the wreck and the cargo of amphorae it carried.

But the real treasure was yet to be found.

In order to keep wooden boats seaworthy, shipbuilders all the way from antiquity through to the present day have applied coatings that keep the water out and slow or halt the ravages of time.

Ancient Roman naturalist Pliny the Elder described a substance derived from ship coatings, noting, "zopissa is the pitch, macerated with salt-water and wax, that has been scraped from off the bottoms of ships."

Although Ilovik-Paržine 1 was in pieces, the wood was preserved well enough to retain traces of the coatings. Charrié-Duhaut and her colleagues took samples and subjected them to a battery of tests to find out what ingredients may have been used.

These tests included molecular, pollen, structural, and statistical analyses to characterize the composition of each of the 10 coating samples taken from the wreck.

"Some regions throughout the Adriatic have particular characteristics that led local populations to develop a specific shipbuilding style," Charrié-Duhaut says. "Only studies like ours offer an overview into these traditions which bear witness to genuine know-how and diverse traditions."

Pitch – a sticky tar derived from heated pine resin – is a known ingredient, and was detected in all 10 of the samples. One of the samples, however, showed the presence of beeswax, just like the zopissa described by Pliny the Elder, mixed in to make the application easier.

Beeswax isn't entirely unexpected, but there was something else the researchers wanted to investigate – pollen. Because pitch is so sticky, it retains traces of pollen from the regions where it was produced and applied.

Their analysis of the pollen in each of the samples returned a wide range of flora from coasts and valleys across the Adriatic and Mediterranean regions – pine, oak, juniper, olive, rockrose, and the daisy family, alongside wetland species like alder and ash.

It's a jumbled mishmash that can't be traced to a single location. It indicates Mediterranean coastal vegetation, shrubby scrublands, wetlands, and even mountainous regions. What this likely indicates is multiple applications of waterproofing from different locations.

"While it seems obvious that ships sailing long distances need repairs, it's simply not easy to demonstrate this," Charrié-Duhaut says. "Pollen has been very useful in identifying different coatings where the molecular profiles were identical."

This is consistent with the statistical analysis, which revealed at least four or five layered applications. The team's findings indicate that the ship was built in Brundisium – known as Brindisi today – in Italy and underwent waterproofing there, but likely had the treatment reapplied at several different ports along its route.

Related: We Finally Know Why Roman Concrete Has Survived For Nearly 2,000 Years

The results offer a fascinating snapshot of Roman-era life and technology, and the sophisticated techniques used to maintain quality in their tools.

"In the context of naval archaeology in the north-eastern Adriatic, a new interdisciplinary approach was implemented to study the protective coating of the Roman Republican wreck Ilovik-Paržine 1," the researchers write.

"This comprehensive approach allows [us] to consider the ship as a whole, understanding the techniques used, the phases of its life, its movements, its environment, going far beyond a simple description of the materials."

The findings have been published in Frontiers in Materials.