Secrets of an ancient Iranian armada sunk off the coast of Greece 2500 years ago are being dredged up by modern archaeologists.

A team from Greece, Canada and the United States has just completed a second expedition to retrieve artefacts from 300 ships of the Iranian King of Kings Darius the Great that were wrecked in a storm off the Mt Athos Peninsula, northern Greece, in 492BC or 493BC.

Aucklanders will be among the first to hear the results today when three of the expedition leaders present their findings in a free public lecture at Auckland University.

In two trips so far, last October and in June, the archaeologists have found evidence of seven ships that went down off the steep coast of the peninsula where local fishing families found two ancient bronze helmets in 1999.

"This has been a dangerous spot for millennia, so there are hundreds of ships scattered around," said Professor John Hale, of Louisville University, Kentucky.

But after 2496 or 2497 years, any remains of the fleet of Darius the Great are likely to be buried under about 2m of mud. "In the Mediterranean there is a teredo worm that eats wood. Any exposed wood is eaten within a matter of months," Dr Hale said. "As soon as silt covers it, it's protected from the worms. But we can no longer see it - we can only see the ballast or the cargo."

Expedition director Dr Shelley Wachsmann said the expedition was "high-risk", but with huge potential benefits if remnants were found of a trireme, the classic fighting ship which eventually gave Athens maritime supremacy after the Battle of Salamis in 480BC.

"Nobody has ever found a trireme," he said. "This is a ship that wrote history, but there are a lot of questions about it."

According to the Western Classics Pages operated by British web designer Andrew Wilson, triremes carried both sails and rowers and were typically 37m long with hard bronze rims.

In battle, three tiers of rowers (hence the name of the vessel) lined up on both sides of the ship. With a full crew of 170 oarsmen, the triremes could reach speeds of 10 knots and ram opposing wooden warships. Although Darius' fleet was under Persian control, the Persians themselves were not sailors and most of their ships were requisitioned from Greek cities in Persian-occupied Turkey.

The site where they were caught in a fierce storm is dramatic, rising sharply from an 1100m-deep trench to the peak of Mt Athos 2033m above sea level.

So far the archaeologists have got down to 600m, using a remote-controlled robotic "rover" to scour 150km of seabed, sending video images back to a ship at the surface.

"If something seems worth checking out, we get into a two-man submersible to check it," Dr Hale said. So far they have found several groups of amphoras, two-handled ceramic jars that were used to carry wine, and a sauroter (literally "lizard-killer"), the bronze tip of a spear that had been preserved in a jar, apparently by an acquisitive ancient octopus.

The team plans to return next year to reach the bottom of the trench. In later years they will move south to four other locations, culminating at the island of Salamis, just off Athens, where the Greeks defeated a later Imperial Iranian Navy led by Darius' son Xerxes in 480 BC.

Auckland University classics lecturer Dr Bridget Buxton, who did her doctorate in Mediterranean archaeology and organised this week's visit, said it was the first time three such "big names" in underwater archaeology had visited New Zealand.

"New Zealand is kind of at Third World level in terms of recognising and protecting our underwater heritage," she said. "There is nothing to stop me going looting the Mikhail Lermontov [which sank in the Marlborough Sounds in 1986] or the Rainbow Warrior [scuttled off Matauri Bay in 1987]."

Dr Wachsmann said he was here partly "to raise interest in the idea that New Zealand, like every other country that has a waterfront, should promote the exploration of nautical archaeology under governmental auspices so that these things are not taken away by private individuals".
Persian Wars, a beginner's guide:

540sBC: Iran occupies Lydia (western Turkey).
499BC: Ionian (Greek) cities on Turkish coast revolt, with support from Athens.
492BC: Iranian armada sails to crush Athens, but is wrecked in a storm off Mt Athos.
490BC: Athens defeats Iran on the Plain of Marathon.
480BC: Iran defeats Greeks at Thermopylae, but then loses at Salamis.
479BC: Iran abandons Greece after defeat at Plataea, near Thebes.

* A public lecture about the expedition takes place at 6.30 tonight at Auckland University.
Venue: Engineering Lecture Theatre 439, 20 Symonds St.