Thera (Santorini) and the Problems of Chronology

So far we have omitted the big problem of Minoan chronology, the problem of the dating of Thera.  Thera, or Santorini,  is an island 60 miles north of Crete – to the modern tourist it is the southern most of the Cyclades islands and the end of the tourist boats from Athens.

Thera volcano

Thera is the remains of a huge volcano. The island, centre right is the centre of the volcano, and the rim can be seen both in the foreground and in the far distance.

Google Earth map to show the position of Santorini north of Crete

Thera is a volcano and in 1628 BC it exploded, sending tens of thousands of tons of dust into the atmosphere. Thera consists of the top part of a caldera of a huge volcano, the central part of which is submerged, and today the steamers sail into this central part and hover inside the volcano, while the tourist buses then crawl up the zigzag road to the present day rim on which the idyllic modern tourist resorts are situated.  In the Minoan period, there was a settlement on Thera known as Akrotiri which was buried beneath the eruption and thus preserved like Pompeii and has recently been excavated.  The culture of the settlement was very like that of the Minoans, and it has often been considered to be a Minoan ‘colony’ — indeed the wall paintings from Akrotiri provide by far and away the best examples of Minoan art.

Thera fresco of lady

Thera: one of the frescos from Akrotiri showing lady in flounced skirt, now in the Thera museum

But what was the date of the eruption of Thera? This is one of the biggest problems of the chronology of the Aegean world because the scientific dating of the eruption and the archaeological dating do not agree; indeed they differ by 100 years or more.  The problem is still unsolved and consequently two sets of dating are given for the eruption: the ‘Long Chronology’ based on the scientific dating, and the ‘Short Chronology’ based on the historical dating. This is a big problem, and in 1989 the links with Egypt and the rest of the Near Eastern world were examined in detail by Peter Warren and Vronwy Hankey.

The eruption of Thera was enormous, and would have had an effect not only on Thera itself, but far wider.  There would have been a major effect on Crete, just 70 miles south where at the very least there would have been a huge tsunami, a wave of water that certainly caused major destruction all along the north coast of Crete, particularly at Amnisos, the port of Knossos. A huge amount of volcanic ash would also have been ejected high in the sky and this would have caused bad weather worldwide.  The nearest event we know, the explosion of Krakatoa in Indonesia in 1883 produced vivid sunsets around the world for several years, and Thera was a bigger explosion than Krakatoa, and would have had a worldwide effect reaching even as far as Ireland and Greenland.

Thera monkeys

One of the largest surviving frescos from Akrotiri showing monkeys climbing in the undergrowth

In 1939 Spiridon Marinatos, the ‘Mortimer Wheeler ‘ of Greek archaeology, and the excavator of Akrotiri wrote an influential article arguing that it was Thera that brought the palace civilisation to a close.  This was soon seen to be wrong: the pottery found in the ruins of Akrotiri comes in the middle of the pottery sequence in the Palaces. In terms of pottery chronology, in LMIb, a ‘marine’ style comes into fashion, when pots are decorated with marine creatures, but this marine style is not found in Akrotiri, so the eruption must have occurred sometime towards the end of LMIa, while the Palaces did not collapse till the end of LMIb. And in the conventional dating, the end of LM1a comes out at somewhere around 1500 BC. There is thus a gap of somewhere around 100 years between the traditional dating of 1500 BC and the scientific dating of 1628 BC.

Three scientific methods have been used to date the explosion: the most popular is tree-ring dating (dendrochronology) which gives an exact date of 1628 BC.  Tree-ring dating is based on the annual growth of tree rings which varies year by year and patterns can be built up which can give an exact date. Occasionally there are bad years when the trees did not grow and tree ring specialists argue that these are the results of volcanic explosions. A number of tree-ring sequences have been built up, notably that by Mike Baillie at Belfast based on the Irish bog oaks and he noted a major blip in the tree ring sequence in 1628 BC which he argued was due to the clouds of dust from the Thera eruption which caused bad weather even as far away as Ireland.   A similar blip was noted in the Californian bristle cone pine sequence, though this was dated a year later in 1627 BC.

A similar scientific technique is the use of the ice cores from Greenland which reveal a deposit of volcanic ash dated to 1642. However the latest research suggests that this is the wrong kind of volcanic ash and refers to a different volcano.

Then there is radiocarbon dating.  This is the technique where the discrepancy was first noted, and there have been a number of datings, the most recent on an olive branch buried beneath the lava flow which has been dated to between 1627 and 1600 BC.  None of these techniques is perfect, but they do provide a sort of consensus that the eruption occurred sometime around 1600 to 1650 BC.

The Astronomical dating

Thera: spouted pots

Spouted vessels of Minoan type now in the Thera museum

The problem is that this comes out at least a century earlier than the ‘traditional’ Minoan dating of around 1500 BC. Yet this date is also scientifically based, on astronomy. When Evans worked out Minoan chronology, it was based on Egyptian chronology, matching up the Egyptian artefacts found at Knossos. And the Egyptian chronology was firmly based on astronomy. The Egyptians had a sacred star, Sirius, which is the brightest star in the sky. However, for half the night, Sirius is invisible and the date it first appeared above the horizon became an important date in the Egyptian calendar, the beginning of the Egyptian year.  Originally it coincided with the beginning of the Nile inundation, but unfortunately the Earth wobbles on a 1460 year cycle, so gradually the reappearance changed, till suddenly it reappeared in 1517 BC which was the ninth regnal year of the pharaoh Amenhotep.

Astronomers can reckon backwards to when this happened. The only problem is, where did the Egyptians take their measurements from: Thebes, or Memphis?  if it was from Thebes, then the year was 1517; if it was from Memphis year was 1537:  1517 is generally preferred. Amenhotep was the second Pharaoh in the New Kingdom, succeeding his father Ahmose, so the New Kingdom began in 1550.

The trouble is, it doesn’t tie up with the Minoan dates. The explosion of Thera, as dated by the pottery found under the volcanic ash on Thera, came in just on the LM1a to LM1b interface: in pottery terms, LM1b is characterised by the ‘Marine’ style, which is not found on Thera.  And this date of 1500 is some 100 years later than the scientific date of 1628 for the explosion. Which is right: volcanic dating, or astronomy? Both sets of dates can be juggled, but the gap of at least a century cannot be juggled away.

It is not for me to arbitrate and if I take the line of least resistance and use the traditional account, I can at least offer a coherent and consistent story. And if the volcanic dating were to be adopted, the whole of Egyptian history, and Minoan history, and indeed the whole of Near Eastern history would have to be revised.

The Minoan Empire is one of the most interesting and most attractive of all the ancient Palace empires. But it finally fell to the Mycenaeans, and it is to the Mycenaeans that we must now briefly turn.

On to Mycenae


24th August 2016, 27th January 2021