Everyone's talking about two tombs just discovered in Saqqara, which is just south of Cairo in Egypt. The tombs are about 4300 years old, and date from the time of Unas, who was the last king of the 5th Dynasty. The contents of the tombs have long since been stolen but hieroglyphics at the entrances show that they belonged to two high officials - a woman who was in charge of music and entertainment for the pharaohs, and a man responsible for the quarries that supplied the stone for nearby pyramids.

The BBC has a nice video showing the tombs, with commentary from Zahi Hawass, head of Egypt's antiquities authority. The tombs themselves aren't particularly stunning but archaeologists are excited because they were found in a little-explored area of Saqqara, and their presence suggests that the necropolis there could be much larger than thought.

Meanwhile a fascinating paper to be published in next month's issue of Tunnelling and Underground Space Technology suggests that the ancient Egyptian tomb diggers must have had a sophisticated understanding of natural ventilation techniques. It's by Don Gribble, a student at Carleton University in Ontario, Canada, and he focuses on tombs dug during the New Kingdom (1570-1070 BC) in the Valley of the Kings, which is hidden in the mountains on the west bank of the Nile, 900 km south of Cairo.

Many of these tombs were dug as corridors into the mountain, with only one opening that served as both entrance and exit. The most impressive tomb found so far, called KV5, was built for the sons of Ramses II. It houses up to 150 underground chambers, and stretches more than 200 metres into the mountain. Archaeologist Kent Weeks surveyed it in 2006 as part of the Theban Mapping Project and found something puzzling: part of the floor of the central chamber had been lowered during the tomb's construction, and later raised again to the original level. Why?

Gribble thinks he has the answer. He points out that because the tombs had only one opening, ventilation would have been a huge problem for the tomb builders. He estimates that a medium size tomb of 500 cubic metres would contain enough air to support 35 workers for just eight hours. Unless the air could be refreshed, they would be forced to stop digging... or die of suffocation.

Luckily the conditions in this part of Egypt are just right for natural ventilation. The air temperature drops dramatically at night, causing a draught of cool air to flow into a tomb, flushing out stale air and dust and replacing it with fresh air. Gribble thinks the alterations to the floor of KV5 show that the Egyptians understood this and used it to their advantage.

KV5 is unique because it has two corridors that point backwards under the entrance, as well as areas that progress forwards into the mountain (you can see plans of the tomb plus a video here). With the chamber floor at its original level, cool air would have flowed forward into the tomb each night, but not into the backwards-pointing corridors. By lowering part of the floor, the workers created a wall that would have acted as a barrier and deflected the cool air into this lower part of the tomb. Once they were done with these corridors, they replaced the floor.

It's a lovely theory. At the moment there's no direct evidence for it, but Gribble suggests that archaeologists could analyse other tombs in the valley with this approach in mind. He also wonders whether any words exist in the ancient Egyptian language to describe this nightly airflow - something like "tomb breath", "living (breathing) rock" or "breath of the tomb Gods". Does anyone know?

If you've ever been to Athens, you're probably familiar with the Tower of the Winds, an octagonal marble tower in the Roman marketplace at the foot of the Acropolis. What's less well-known is that it held one of the largest and most elaborate water clocks of Greek and Roman civilisation.

The tower is one of the only buildings from ancient Greece or Rome that has never been buried or demolished, or even lost its roof. It was built at the beginning of the first century BC by a Macedonian astronomer called Andronicus of Cyrrhus. Carved on its faces are eight winged demigods, representing each of the eight winds, with a sundial beneath each one.

The inside, by contrast, has been completely gutted and the only sign of its original function is a mysterious pattern of holes and grooves carved into the floor and walls. In Roman texts, the tower was referred to as an horologium, which means "hour indicator". And the ancient name of the spring that runs above the tower in the hill of the Acropolis is Clepsydra, which means "water thief" and was a name often used for water clocks.

This much is fairly easy to find out. But what did this water clock look like? For nearly a century after the tower was first described by archaeologists in 1870 scholars didn't even attempt to answer this question because its mechanism had completely disappeared. Even today, descriptions of the tower tend to give only the shadiest of details about the clock itself. While I was researching Decoding the Heavens, however, I managed to unearth a couple of papers from the 1960s, in which a British science historian called Derek de Solla Price - better known for his work on the Antikythera mechanism - reconstructed it. The papers were published in the American Journal of Archaeology in 1966, and in the April 1967 issue of National Geographic (neither are online I'm afraid).

Price reckoned that deciphering what the floor markings once supported was like "recreating the workings of a suburban kitchen in an empty room, using the relative positions of the sockets, pipe holes and rectangular floor stains as evidence". So he drew a plan of the holes and grooves in the tower, then compared them to the water clock designs described in ancient texts. He found a match.

Water from a nearby stream poured into container that was engineered to keep a constant water level - either by overflow pipe near the top or a ballfloat that blocked the inflow pipe when the tank was full. Water then dripped from hole in the bottom of this container at a constant rate into a cylindrical vessel beneath. The rise in this water level over the day was used to measure the passing hours, and it was emptied and started again with each new dawn.

This type of clock was designed by the Greek engineer Ctesibius in the third century BC, and used throughout the Greek and Roman worlds. But the scale of the Tower of the Winds suggests that this one was huge.

A float in the measuring tank would have turned an axle as it rose, and this in turn was connected to a large bronze disc, marked with the constellations in the sky, which rotated behind a set of curved wires that represented the position of the horizon and the hours of the day - it might have looked a little like the Prague astronomical clock (pictured), although driven by water and not clockwork. From the front, an observer would see the Sun and stars riding clockwise through the sky as time passed, mirroring the movements of the heavens. Price also found channels in the floor where the overflow from the water tank fed three fountains, and grooves that held marble railings to keep spectators away from the clock's machinery. Knowing the Romans, the clock was probably also surrounded by elegant statues.

The gleaming bronze star disc turning inexorably and mysteriously in line with the sky must have been the main attraction of the bustling Athens marketplace. This was much more than just a timepiece. It was a spectacular celebration of the beauty of the heavens, and of man's understanding of it.

Time for another shipwreck story - scientists think they have solved the mystery of why the Mary Rose sank.

The Mary Rose was Henry VIII's finest warship, but she sank on 19 July 1545 while engaged in battle with the French Fleet, just off the southern coast of England. She took 415 men to their deaths, and Henry himself watched her disappear beneath the waves. But why did such a well-respected vessel sink so suddenly? The French navy claimed they had holed her, while the English said she tipped over while making a sharp turn, causing water to pour in through her open gun ports. Other theories have included everything from an unruly crew to an outbreak of dysentery.

Now researchers analysing the remains of some of the crew have come up with another idea - she sank because many of her crew were foreign, so language difficulties meant they were unable to understand orders in the heat of battle. Lynne Bell from the School of Criminology in Simon Fraser University in Burnaby, Canada, and her colleagues analysed oxygen isotope ratios in the bones and tooth enamel in 18 of the sunken sailors, and what they found was completely unexpected. Most naturally occurring oxygen exists as 16O, ie with 8 protons and 8 neutrons in the nucleus of each atom. But there are also tiny amounts of 18O, which has two extra neutrons. Water molecules containing 18O are heavier than normal, and condense more easily. So as moist air masses are carried away from the equator by prevailing winds, the heavier molecules are lost more easily as rain. The closer you get to the poles, the less 18O there is in the water. This ratio is carried over into the plants that grow in a region, and anything that eats those plants, so by looking at the ratio of 18O in someone's skeleton, you can tell where they spent most of their life.

Bell and her colleagues found that 30-60% of the sailors on the Mary Rose had 18O ratios too high for them to have been from England. They came from much further south, somewhere like Mediterranean Europe. In that case, their English probably wasn't great. As the Mary Rose turned, perhaps they weren't able to understand the order to close the gun ports in time to save her from sinking.

Those of you alert to archaeology news may have heard this before - a Channel 5 documentary mentioned it in the summer. But Bell's study is now being published, in next month's issue of Journal of Archaeological Science, so I thought it was worth mentioning again. Historians have uncovered documents refer to 600 Spanish mariners who had been stranded penniless at Falmouth 4 months earlier, and taken into the service of the King. Perhaps Henry, struggling to create Britain's first real navy in response to the French threat of invasion, was forced to use foreign crew on his prized warship - with tragic consequences.

Bell's detective work is about to hit the headlines again, by the way. She has also been studying the remains of a killer called the Mad Trapper who was caught and shot by the Mounties after a dramatic manhunt across the Canadian Arctic in 1932. This is where the expression "The Mounties always get their man" comes from. But who was he? Bell has carried out similar isotope tests on his exhumed body, to check his geographic origin and diet in the hope of establishing his true identity. The results are to be revealed in another documentary, apparently due to be shown on the Discovery Channel this month.

I was on Radio 3's Night Waves programme on Monday to chat with Jim al-Khalili about his new TV series Science and Islam (you can hear it here for the next few days). Jim is a physicist at the University of Surrey, trained in the western scientific tradition, but he was born in Baghdad. In the series, he explores the contribution of the Islamic world to the history of science. Are there Medieval Muslim scientists who should be spoken about in the same breath as Galileo, Newton or Einstein, he asks.

I've written here before about the influence of Islamic science and technology, and Jim is absolutely right that the achievements of these scholars are under-recognised today, in their home countries as well as the West. We're taught that once the ancient Greek and Roman civilisations fell, not much of importance happened in science until 1543, when Copernicus suggested that Earth orbits the Sun, and the anatomist Vesalius corrected longstanding misconceptions about the human body.

But during this time the Islamic world covered a vast kingdom that at its height stretched from Spain to northern India. Within this region, Muslims, Christians, pagans and Jews all worked together in the common language of Arabic. They had access to past knowledge from Greek, Egyptian, Persian, Indian and Chinese scholars, and starting in the eight century the Muslim rulers began a huge effort to translate, synthesise and disseminate this knowledge. It was a wonderful flowering of civilisation, openness and learning.

Much of the ancient knowledge that inspired European scientists in the 16th century reached them via Arabic translations, and for this alone western science owes a huge debt to its Islamic counterpart. And in many areas scientists working in the Islamic world improved significantly on the learning they inherited. Take the 13th-century astronomers of the Maragha school who developed mathematical techniques to describe the motions of the planets that were later used by Copernicus. Or the 9th-century Baghdad scholar al-Khwarizmi, who invented algebra (the picture shows a page from his book on the subject). In fact, pretty much any scientific word starting with "al" - such as alcohol, alkali, algorithm - probably comes from Arabic. 

Jim's series is showing on BBC4, starting on 5 January. It's a joy to watch - beautifully shot and full of fascinating ideas, stories, people and places. I'm so pleased that he's drawing attention to this crucial chapter in the history of science. But while Jim emphasises the unprecedented feats of Islamic science, I would argue that the big achievement of this period was synthesis, not revolution.

The Maragha astronomers developed the maths to improve Ptolemy's models of planetary motion, for example, motivated by the idea that celestial orbits were divine and should involve only perfect circles. But for the most part they didn't attempt to make accurate astronomical observations and then explain what they saw. Chinese astronomers wrote detailed descriptions of the Crab Nebula, dramatically formed by a supernova in 1054. But scientists in the Islamic world barely mentioned it. And they never questioned the idea that the Earth was at the centre of the universe.

It was the Europeans, for whatever reason, who broke free of their dependence on ancient texts and finally made the leap to seeing knowledge as something to be gained by observing and experimenting on the natural world. Now science, not God, was the fundamental source of knowledge. That really was a revolution.

I posted the other day about a feature I've written for this week's issue of New Scientist, about Archimedes' links to the Antikythera mechanism. The device embodied the ancient Greeks' latest knowledge about the nature of the cosmos, so I was happy to see another feature in the same issue that discusses state-of-the-art thinking from today's cosmologists. It's the idea that our universe did not begin with the Big Bang. Instead, it bounced into existence when a previous universe collapsed in on itself. Rather than collapsing to nothing, this previous universe shrank to a fiery state of almost unimaginable density and temperature (equivalent to squeezing a trillion Suns into the space normally occupied by a proton), then rebounded and started expanding again. Physicists think this could be part of an eternal series of expansions and contractions, with no beginning and no end.

There's as yet no experimental evidence for this idea but the model is gaining increasing support - alternative theories simply break down when they get too close to the moment of the universe's creation.

The Greeks may not have been surprised by the Big Bounce. One of their main schools of philosophy, Stoicism, held that the history of the universe was an endless series of cycles, in which the entire cosmos was periodically destroyed in a huge fire, or "conflagration", before being created anew.

An extremely rare astrolabe quadrant has been rescued - for the second time. Back in 2007, I wrote a news story for Nature about this intriguing device after it was plucked from a junk pile during building works in the historic British city of Canterbury. Foundations were being dug for an extension to a restaurant that was housed in a period property, and Andrew Linklater of the Canterbury Archaeological Trust, who was assigned to watch over the works, found the dirty brass plate nestled among shards of pottery in a 14th-century rubbish pit.

Linklater couldn't identify the plate, so he took it to the British Museum. The experts there "held their hands up and went wow", he told me. It turned out to be only the eighth astrolabe quadrant ever discovered. The way it had been found was even more unusual - the device would have been the height of technology at the time, and such instruments are usually handed down through collections, not found discarded in archaeological sites.

Astrolabes were used for making astronomical observations and allow their owner to tell the time and calculate latitude. They are normally circular, but the rarer quadrants were "pocket" versions - more complicated to use but easier to carry around. Back in the 14th century, the street where the quadrant was found was lined with inns for pilgrims coming to Canterbury, so perhaps it belonged to one of these travellers.

I'm writing about it again now because the UK Reviewing Committee on the Export of Works of Art and Objects of Cultural Interest has just released its annual report. This committee defers export licences on precious artistic and cultural artefacts in danger of being sold abroad, so that they remain in the country until money can be raised by a British buyer (I bet the Greek government wishes it had had such powers back when the Elgin marbles were being shipped to the UK). Eight items were saved last year, and the Canterbury quadrant was one of them. When I wrote my news story, the quadrant was about to be sold by London auctioneers Bonhams, and it was expected to net the restaurant owners between £60,000 and £100,000. The British Museum wanted to buy it but was outbid by an anonymous telephone bidder, so the government acted. In the end, thanks to the temporary ban on export (and some generous grants) the British Museum was able to buy the quadrant at a second auction in July 2008 - for £350,000!

The extension to the restaurant is now complete by the way, and the owners have apparently named it the Quadrant Bar. 

This week's issue of New Scientist includes a feature I've written about the Antikythera mechanism, you can read it for free here. I wrote a long article about this 2000-year-old device for Nature a couple of years ago, which described researchers' efforts to decode it. I wanted to do something different this time so I focused on the possibility that Archimedes could have been the original inventor of this technology (as suggested by new readings of the inscriptions published this summer) and on how astronomical models like the Antikythera mechanism existed alongside a parallel tradition of modelling living creatures such as people, animals and birds. These models affirmed the ancient Greeks' idea of a divine order, as well as being used to demonstrate basic physical laws in pneumatics and hydraulics. The Greeks have often been derided as wasting their technical ingenuity on mere toys, but as I say in the feature, these models weren't toys, they were a route to understanding and demonstrating the nature of the universe - they represented a way to get closer to the true meaning of things. To what better use could technology be put?

New Scientist also has a souped-up version (see above) of the video I posted a couple of weeks ago showing the first complete reconstruction of the Antikythera mechanism, plus some new images and graphics. The Guardian has picked up on the video today as well, with this blog post. "I defy you not to be amazed," says Guardian science correspondent James Randerson.

Here's a quick note following on from my post a couple of weeks ago about the Book of Secrets, a mysterious eleventh-century Arabic manuscript containing descriptions and drawings of more than 30 ingenious devices, including water clocks, automatic calendars and war machines. Researchers at an Italian company called Leonardo3 have spent months deciphering it and creating a virtual interactive version of the book, and the results of their work are on display at the new Museum of Islamic Art in Qatar.

I didn't have any pictures of the Book of Secrets at the time, but Massimiliano Lisa, one of the curators at Leonardo3, just emailed me to say that there's now a lot more information available, plus videos and photos of the exhibition, here. The researchers have built two of the devices described in the book, the Clock with Three Characters and the Fortress Demolisher. Many others have been reconstructed virtually, including an automated model that acts out a love fairytale involving some evil snakes!

The designs are beautiful - many of them works of art in their own right. For those of us who can't make it to Qatar, you can buy a copy of the manuscript along with a book and interactive DVD. I know what's going on my Christmas list :-)

In the late Bronze Age, around the 14th century BC, a richly stocked cargo ship sank off the south coast of Turkey. The wreck, called Uluburun, was rediscovered in 1983, and archaeological expeditions have yielded an astonishing collection of artefacts. She was carrying copper and tin ingots, plus exotic raw materials such as ebony, amber, ostrich eggs, elephant ivory and hippopotamus teeth, while manmade artefacts ranged from pottery, tools and fishing equipment to weapons, jewellery and a gold scarab bearing the name of the Egyptian queen Nefertiti. The huge wealth of the cargo suggests that this was a royal vessel, perhaps taking gifts to the Pharaohs of Egypt. 

But despite all this treasure, the ship's origin has been a mystery. The items on board came from at least nine different cultures, including Canaanite, Mycenean, Egyptian, Cypriot and Babylonian. All experts have been able to say is that she probably sailed from either the mines of Cyprus, or the coast of Syria or Palestine.

I just saw a lovely little paper in last month's Journal of Archaeological Science that reports a new clue - from a young mouse that went down with the ship. Researchers sifted through loose sand and sediment brought up from the wreck and found a tiny jaw bone, just a centimetre long. Thomas Cucchi of Durham University analysed it and concludes it comes from a house mouse (Mus musculus domesticus). It's pretty certain that mice have spread across the Mediterranean in ships throughout ancient history but this is the earliest direct evidence of it, in fact that only other such stowaway ever found is a brown rat (Rattus norvegicus) from an 18th-century French galleon that sank off Corsica.

What's more, Cucchi reckons that a tooth from the Uluburun stowaway is most similar in shape to those of house mice that live in Syria today. Mice were likely to be brought on board with shipments of grain, so he tentatively concludes that the ship started her journey at the Canaanite port of Ugarit, on the Syrian coast. Ugarit was a huge international trading centre in the 13th and 14th centuries BC, and probably the only place on the Syrian coast where a ship could have taken on board large shipments of both grain and metal ingots.