In 1900, sponge divers working near the Greek island of Antikythera accidentally discovered a 2,000-year-old mystery.
Dressed in a canvas suit with a helmet made of copper, Elias Stadiatis plunged through the cool ocean depths, in search of the soft sponges he had spent his career gathering.
But as he reached the rocky bottom at a depth of about 50 metres, he uncovered a long-forgotten tragedy.
Hidden between layers of debris on the ocean floor were what appeared to be rotting corpses and horses.
Stadiatis immediately began signalling to the crew above and was soon dragged back to the surface, apparently shaking with fear and mumbling about "seeing a heap of dead people".
They feared Stadiatis was delirious, suffering from nitrate poisoning or seasickness.
So his captain, Dimitrios Kontos, went down to see it with his own eyes, re-emerging some time later with the arm of a bronze statue. Or so the story goes.
What Stadiatis had mistaken in the darkness for the bodies of humans and animals were in fact sculptures and artefacts from an ancient shipwreck.
Kontos's team moved on, returning some time later to attempt a retrieval of the ship's treasures and alert Athens to the archaeological goldmine.
Almost immediately, a fleet of ships was sent to the island — including the Hellenic Royal Navy vessel Mykali, the civilian steamship Syros, and later the Navy torpedo boat Aigialeia.
For several days, a group of sponge divers took turns descending to recover what would become significant clues into ancient merchant life.
The team, barely aware of the dangerous impact these dives had on their bodies, continued to work through hazardous conditions: rough storms, freezing winter temperatures and swirling currents.
Within a year, two men were severely injured and another diver died. By the time the operation ceased, only five men were still fit to dive.
"The regrettable thing is that, considering to what stage the work has arrived, the divers refuse to do further dives," wrote an eyewitness to the excavations in 1901.
"The excavation of the rocky concretion soil frightens them, they no longer have a hope, they say, of discovering other statues."
Since then, the treasures of Antikythera have become legend.
Nearly 120 years later, another excavation hopes to uncover the secrets still buried within the ship and possibly recover more treasure.
Most 'technologically complex object' ever found from ancient world
Despite working with only the rudimentary materials available at the time, the diving team from the 1901 excavation uncovered a priceless haul of artefacts and statues at a depth of between 42–52 metres.
Antique glassware, exquisite jewellery, solid marble and bronze statues, and ancient coins were among just some of the treasures discovered at the site along with a misshapen hunk of rock.
It was months before the corroded lump, roughly the size of a large dictionary and covered in green spots that looked like mould, was finally cracked open to reveal a mess of gearwheels, inscriptions and a ring divided into degrees.
But it would take more than a century for scientists to better understand the mechanism.
"This is the first shock because anything from ancient Greece simply shouldn't have gear wheels," professor Tony Freeth at the University College London told the BBC.
The gears, which were made of bronze and had teeth that were a millimetre long, calculated the cycles of the cosmos — the sun, the moon and the movement of the planets against the stars.
It became known as the Antikythera mechanism, a mechanical computer that predicted astronomical events like eclipses with startling accuracy for its time.
It's considered to be the most "technologically complex object" ever found from the ancient world, though only a third of the original survives.
It worked like this: if you wanted to know what the position of the moon would be in five years' time, you would turn the handle and "it would tell you almost immediately," Professor Freeth explained.
A team of new divers arrived in Antikythera in the 1970s with the hopes of finding more treasure.
Led by famous adventurer Jacques Cousteau, they recovered hundreds of objects in 27 days, including ceramic vessels, gemstones, fine glassware, and human skeletal remains.
But when the excavation wrapped up, many key questions remained: who did the ship belong to? Why was it carrying so much treasure? And perhaps most interesting of all, why did it sink?
Scientists searching for these answers went back to the shipwreck in 2012, on an excavation called Return to Antikythera and led by the Ephorate of Underwater Antiquities.
A new phase of this expedition, conducted by the Swiss School of Archaeology under the direction of Dr Angeliki G Simosi, will now run until 2025.
"The approach is really an archaeological one. We want to understand the site, we want to understand the history, and to learn about how this disaster happened," Lorenz Baumer, a professor of archaeology at the University of Geneva and one of the lead researchers on the project, told the ABC.
As the research team search for clues at the bottom of the sea — with the smallest hope of locating more fragments of the mechanism — the task has become something of a Herculean effort.
Earthquake and underwater balloons helping to uncover a mystery
Excavating a shipwreck is not a simple job. The diving, equipment and vessels required can be costly and the process itself quite time-consuming.
Divers working on the Antikythera shipwreck in its most recent survey from May 23 to June 15 could only work at the base in increments of 30 minutes.
They also had the tricky task of moving large boulders that have steadily fallen from Antikythera's steep cliffs over the course of 2,000 years.
Scientists suspect a major earthquake, which struck hundreds of years after the shipwreck, may have dislodged some of these eight-and-a-half-tonne stones.
The boulders likely protected the treasure buried beneath, but the effort of lifting them while 50 metres underwater has required a mix of precision, skill and advanced technology.
"These rocks are laying on the sea ground since at least 1,500 years, maybe more, so you have natural deposits around them [created] by mussels [and] by corals," Professor Baumer said.
Divers must first break the rocks free, just a little bit, to open them up — a process of "very precise rigging," Professor Baumer says — before they can tie ropes around the boulders.
The ropes are attached to underwater balloons, designed by the Swiss watchmaker Hublot and filled with air by a compressor sitting on a ship above, which help to lift the rocks so they can be moved to the sea floor.
By moving these boulders, the team hopes to explore formerly undiscovered areas of the ship.
Already, divers have found human teeth, a marble plinth for a statue, a lead collar for an anchor, and the weathered, marble head of a bearded male figure believed to be the Greek hero, Hercules (also known as Herakles, or Heracles).
Bigger than life size, the missing head may belong to the Herakles of Antikythera statue currently on display in the National Archaeological Museum in Athens, according to Mr Baumer.
"[The body was] found in 1901, but there is no information available where exactly it [was] found. And now we have [the head]. So we know exactly where it comes from," Mr Baumer said.
The exact position of each finding is being precisely documented and will be integrated into a 3D model of the site, which will hopefully give scientists a better understanding of the wreckage and the conditions of the ship's sinking.
"Every bit of information we can collect, we are putting it together, integrating them into a 3D model," Mr Baumer said.
"And this will [give us] a more comprehensive, a more complete picture, and then we can really start."
What happened to the 'Titanic of ancient times'?
The Mediterranean was a hive of activity when the ship was in its prime in the first century BC, with vessels of all makes and sizes crisscrossing their way to ports and harbours in Africa, Italy and the rest of Europe.
The island of Antikythera lies at the centre of this ancient transport hub despite famously drowning ships.
"You can imagine enormous traffic by ships going all around the Mediterranean, transporting goods, food, artworks," Mr Baumer said.
In a sign of just how busy this region was, the Antikythera shipwreck was only the first of a series of ancient shipwrecks to be identified in the eastern Mediterranean over the course of the 20th century.
For decades, speculation has swirled around who may have ordered the "Titanic of ancient times", with some pointing the finger at famous Romans who would have had the means and power to order a haul of that size.
"I can imagine someone like Lucullus, who just had conquered Asia Minor... taking one of these massive grain ships and repurposing it," archaeologist Brendan Foley, who worked on the Antikythera Shipwreck from 2012 to 2018, told the ABC.
He suspects, if this was the case, the ship may have been loaded up with the spoils of war to be brought back for a victory parade in Rome.
Others suggest the ship may have been transporting antiquities for a number of buyers.
When asked if it could have been pirates, who may have seized the treasure and fallen into trouble on their way back, Mr Baumer is quick to rule it out.
"We have in the first century [BC], after Pompey had cleared the problem of the pirates in the Mediterranean, we are in a peaceful situation. Robbery at that dimension, we really do not expect," he said.
Uncertainty also remains over what may have caused the ship to wreck, with some hypotheses ranging from a freak storm to a risk-taking captain or the possibility it was carrying too much weight, Mr Baumer said.
"In archaeology, we always have the final product, whenever you make an excavation, you have the last step," he said.
"And to understand how it came to that last step, you have to try to do the analysis to understand all the previous episodes that led to that situation."
With marine archaeology's history firmly rooted in treasure hunting — "people want to find gold" and billion-dollar hauls, Mr Foley says — uncovering the mystery behind ancient shipwrecks has not always been a priority.
It's a problem marine archaeologists continue to grapple with, despite the cultural and historical insights these excavations offer.
But, as Mr Foley argues, the story of the world, of its history and how civilisation starts, is just as important.
Back at Antikythera, some of those tales may still lie at the bottom of the ocean, waiting to be discovered.
