In 2007, evidence of a deep-water shipwreck was detected during an offshore remote-sensing survey conducted on the fringes of Xlendi Bay in Gozo, Malta. This anomaly turned out to be the remains of a Phoenician cargo vessel dating back to the 7th century BC, a rare and hugely significant find. Due to its location, the team named it the ‘Xlendi wreck’. At 110m below sea level, the wreck is extremely challenging to dive, and it was only in 2018 that the first underwater excavation took place.
An initial survey of the wreck in 2014 confirmed that the upper layer of cargo lay exposed on the seabed, including dozens of amphorae (storage jars) and grinding stones used to make flour. Then, in September 2018, a team of highly trained technical divers led by maritime archaeologist Timmy Gambin was able to recover a small sample of artefacts for closer study. These objects, including a Tyrrhenian amphora, a small urn, and a flat-bottomed amphora of possible Greek origin are currently on display at Heritage Malta’s Gozo Exhibition Hall.
Who were the Phoenicians?
Regarded as some of the most successful maritime traders of the ancient world, the Phoenicians occupied the Levant region of the eastern Mediterranean, in what is present-day Lebanon and south-western Syria. Little has survived of Phoenician literature, so much of what we know stems from either the archaeological record or Greek and Latin writings. Due to the mountainous topography of the Levant, the most effective way for the Phoenicians to achieve economic prosperity was through maritime trade, and thus they became skilled sailors who navigated using the stars – they have even been credited with inventing the concept of celestial navigation.
Despite their reputation as successful sailors, few Phoenician shipwrecks have been discovered in the Mediterranean. Ancient accounts and surviving iconography reveal that they used three types of ship: one for combat, with a square sail and two banks of oars, and two types of trading vessel. The Xlendi wreck is certainly a trading vessel; it must have measured approximately 14m in length.
Despite the challenges of the pandemic, the international dive team lead by Timmy Gambin arrived in Gozo in August 2020, with all the necessary COVID-19 safety measures in place. They had two main aims: to excavate some more objects on the seabed and to record the ship’s ballast in situ. A ship’s ballast is the material used to provide stability. Sometimes rocks are used, but this need is often filled by using cargo, as it was on the Xlendi wreck.
Over five weeks of fieldwork, a substantial quantity of cargo was recovered, including a number of complete amphorae, ceramic fragments, and smaller jugs and urns. The amphorae were transported in a custom-made cage attached to powerful lifting bags. Using a submersible hydraulic hose lowered to the seabed enabled the team to excavate the next layer of the wreck while systematically recording their progress. They were able to lift wooden fragments from the lower levels, and discovered evidence of a mortise and tenon joint: an ancient shipbuilding technique used to assemble the hull of a ship. This is one of the earliest examples of this joint type being used for hull construction in the Mediterranean.
Given the inaccessibility of the Xlendi wreck, and indeed submerged sites in general, Heritage Malta has also opened a new online museum to showcase the Phoenician shipwreck along with other underwater discoveries. Thanks to recent improvements in recording underwater archaeological sites, 3D models of the wrecks can now be explored in full virtual reality with 360° views. As the pandemic has forced numerous museums to shut their doors, making museums and archaeological sites digitally accessible has become all the more important.
But what does it require to create these models? And how can divers photograph the wrecks in sufficient detail to translate them into virtual museum exhibits?
Digital dive into history
The use of new technologies to record underwater sites is not a recent phenomenon. This has long been a focus for maritime archaeologists, as underwater sites can easily fall victim to an ‘out of sight, out of mind’ attitude. More recently, the use of digital technology to create 3D models of these important discoveries has gained major traction, while Malta has become a centre for underwater cultural heritage thanks to the number of offshore shipwrecks and crashed planes.
We have come a long way from the breath-holding techniques, dive helmets, and diving bells once used with the sole intent of retrieving archaeological treasures from shallow waters. In 1943, engineers Jacques-Yves Cousteau and Émile Gagnan invented an apparatus that made possible self-contained underwater breathing. Since then, archaeologists have been able to spend more time interacting with and recording underwater sites. In Malta, Honor Frost’s excavation of the so-called ‘Mortar Wreck’ in the 1960s is considered an examplar of scientific underwater excavation.
The Mortar Wreck is a 3rd-century AD Roman shipwreck located in Mellieh¯a bay on the northern coast of Malta. Reports of discoveries there date back to 1959, and the presence of a wreck was established in 1964. A preliminary investigation of the site was carried out by Honor Frost in 1967. Frost was a pioneer in underwater archaeology, and among the first to promote it as a discipline combining diving with archaeological practice. Her excavation and survey of the Mortar Wreck took an innovative approach to the scientific recording of a wreck site, meticulously documenting finds, the site, and the surrounding context. Frost’s scientific diligence enabled the University of Malta to return to the bay. A remote-sensing survey was conducted in 2010, a diver survey in 2012, and two seasons of fieldwork in 2013-2014. On a local scale, Frost’s excavation, survey, and publication of the Mortar Wreck is widely considered to be the first scientific underwater investigation conducted in Malta.
Fast forward 50 years, and one of the most important advances in digital underwater archaeology is the use of 3D capture of data by photogrammetry and laser scanning to record the visible part of wrecks with unprecedented accuracy.
Photographing a deep-water wreck
Back in 2014, prior to the first dives on the Xlendi wreck, the team used a manned submersible to descend into the depths and photograph the site so that the images could be used to create the 3D model.
Since 2016, this task has been carried out by specialised rebreather divers. As the Xlendi wreck is so far below sea level, it is a very demanding dive. In order to capture a sufficient quantity and quality of images to build the detailed 3D model, multiple dives were required.
For the Xlendi wreck, divers would take around eight minutes to descend and had a maximum of 15 minutes to photograph the site. To ensure their safety, they would then require three hours of decompression before they could return to the surface.
The 3D diving team, John Wood and Kari Hyttinen, told us about the challenge of recording the site in such a short time period: ‘We have managed to work around the 12- to 14-minute limitation in a number of ways. When recording the complete site at the start and end of a season, two divers each record half the site plus sufficient overlap to ensure that nothing is missed, and a single model is created from the combined data set. In order to record just the excavation area, which is done on a daily basis, the dive time is sufficient, assuming everything goes to plan.’
Visibility can also be an issue when the sediment is disturbed, so the 3D dive team are either the first or last to descend to the wreck, so they can take clear pictures. If they go last, enough time is calculated for the sediment to resettle and visibility to return.
During their time on the Xlendi wreck, the divers used high-resolution mirrorless cameras in waterproof housings. Strong lights were essential to illuminate the wreck so it could be seen in its full glory, and so that the colours would not be lost due to the filtering effect of the water.
Making a 3D model
Once the team captured enough images of the Xlendi wreck, they were able to produce the 3D model using photogrammetry. This involves taking measurements of the shipwreck’s visible features through the analysis of overlapping photographs in order to produce a 3D model. Due to the size, complexity, and visibility of the Xlendi wreck, thousands of images were captured manually each day.
In order to be converted into a detailed 3D model, these images would be loaded as a single batch into software that is also capable of automatic camera calibration. This method is relatively low-cost, as it does not require significant training or overly expensive equipment. However, it is a laborious task and extremely time-consuming, particularly for larger and more complex underwater sites.
According to John and Kari, ‘The actual dive for recording data is only a part of the overall process, and as a team we have managed to improve and fine tune the whole process of site-preparation, daily recording, and data-processing to a point where it has become quite a routine task with highly predictable results. It is this whole process of continual learning and improvement that has personally given us the most satisfaction.’
A resulting 3D model of the Xlendi wreck has been uploaded to Heritage Malta’s Virtual Underwater Museum. It provides an accurate picture of how the wreck appeared on the sandy seabed before any excavations took place.
The Phoenician shipwreck is just one of the highlights of Heritage Malta’s new virtual museum, which showcases a selection of 12 shipwrecks and crashed planes around Gozo and Malta. Members of the public can explore the 3D models of each wreck, including the option to use a virtual-reality headset.
Viewers simply click on the image of the wreck they want to investigate and load the 3D model, before navigating using the cursor and zoom functions on their device. There are plenty of images and videos to accompany each model, along with more information about the discovery of the wrecks and their historical contexts.
To start exploring the museum, visit https://underwatermalta.org/.
With thanks to Heritage Malta, the University of Malta, the Malta Tourism Authority, and the rest of the Virtual Museum team: https://underwatermalta.org/the-team/.