When Cape Town maritime archaeologist Bruno Werz was excavating an underwater 17th century wreck in Table Bay, he expected, and found, artefacts like broken pottery, a few teaspoons and the occasional cannon ball.
But as he excavated deeper into the sand on the seabed, he was astonished to find a Stone Age hand axe lying in the sediment - probably just where it had been dropped one day, 300 000 to 1,4 million years ago.
"It came as a bit of a shock, because I was focused on finding historical artefacts, not anything prehistoric. I came to the surface very excited, but the other divers didn't understand what I was going on about," said Werz.
His excitement became greater when he met UK oceanographer Nicholas Flemming at an international conference. "I dropped the hand axe in his lap and he nearly fell over.
"When I told him where I had found it, he said: 'This is world news'."
It turns out that this is the oldest human artefact found under the sea, where it had been used, anywhere in the world.
Prior to Werz's find, the oldest underwater artefacts - found in the Mediterranean - were dated about 45 000 years old.
Near the hand axe, Werz found fossil rhino bones and a rhino tooth.
In later months, divers Christopher Byrnes and Michael Barchard found two more hand axes in the same vicinity.
"At the time the axes were dropped by Stone Age people, the sea level around South Africa was about 10 metres lower than at present," said Werz. "There are indications that there was a river delta where Table Bay is now, which would have created a fertile valley where animals like buffalo and rhino roamed.
"The hand axes would probably have been used by early humans to butcher carcasses of dead animals and possibly to kill animals," said Werz.
One of the axes, made of local quartzite, still has a very sharp edge indicating that it was quickly covered by sediment on the same spot where it had been dropped.