The land before athenians

When I think about Athens I usually have this amazing time-travel view of the Acropolis with its ancient ruins, flowers smell, wind in my hair, beautiful sunsets and history pretty much everywhere. I also have this feeling of freedom, a feeling that accompanies me when I am traveling or going for fieldwork. But Athens is much more than that and it has a history that goes far back in time, beyond human history, in a period when all we see now as Attica was in fact the bottom of an ocean-Tethys.

Evening view from the top of the acropolis to W through the Propylaea (dec.2018)

If you ever had the curiosity to look at the 'stones' around, or the topography, you will realise that Athens has several hills caped with limestones, similar to Rome. They are giving it this picturesque view and they are also the reason inhabitants chose it as a settlement in the first place. Among this hills (6 or 7, or more-depending how you count them) the Acropolis hill is the most proeminent and if we focus on its lithology (rocks assemblage) we see a pile of limestones (carbonates) sitting on a more plastic succession of shales (very fine grained, clayey material) and sandstones (cemented sands). The carbonate part is known in literature as the Tourkovounia Formation and it was formed during the first part of Upper Cretaceous during Turonian and Cenomanian stages (100-89 Ma), while the shale is known as Athens schist and it was deposited during Maastrichtian, the final stage of Cretaceous (72-66 Ma). The Athens schist is not a classical schist rock type, but it was named liked this due to the low grade of metamorphism the rocks register, as consequence of the faulting and thrusting process that occurred after deposition.

Geological structure of the Acropolis (south view). You can see the older limestone sitting on the shales, the contact between them ad several new faults that affected the entire structure.

So we have a pile of older rocks sitting nicely on younger rocks. What happened?! Well, Tethys ocean started already to close during upper Cretaceous and the large basin that use to be during Triassic and Jurassic was divided into smaller basins, one of them in our area. As a consequence of african and european plates collision, sediments were compressed and pushed towards north. Some 15-20 millions year after our shales formed, during the Eocene, the older limestones were faulted and thrusted over the shales (which are very plastic and accommodate movement better) in the form of a nape. This nape was overturned (making possible the contact between limestone and shales as we see it) and then eroded in time.

A, C: contact area and decollement surface which has breccia type filling (blocks of limestone were broke from the formation and agglutinated by the thrusting fault on its path). With green is marked the contact and with red the younger faults. B: direct contact, D: an area where the limestones were completely eroded.

Starting from Miocene (~the last 15 million years), the entire area was subject to an extensional regime which created several basins (among what we see today as Athens urban area) through normal faulting. As a result of faulting, the nape/napes in Athens area were truncated and eroded. The neogene basin was covered by sea and filled with younger marine sediments, plus the sediments eroded from the mountain ranges around Athens (Parnitha, Aigaleos, Penteli and Hymettos).

Simplified sketch with the tectonic evolution of the area since Cretaceous to present day.

Around 9000 years ago the Acropolis started to be inhabited and then the surroundings. It was a naturally fortified hill, had acces to sea and plenty resources around it. The Acropolis was treasured not only for its strategical position but also for its fresh water springs. The limestones above were absorbing the precipitations and channeled them through the fault system towards the base. Thus, in the contact area between limestones and shales the water was discharged as springs. The largest one was in the NW side and the Athenians named it Clepsydra or the "stolen water". The water wasn't available all the time due to the precipitations regime. Probably the water was missing over the summer and beginning of autumn. In the present the springs are not active anymore due to climate changes.

Clepsydra discharge/spring, the largest on the Acropolis. For details and more interesting stuff about the Acropolis's karst and geology I recomand:

https://www.researchgate.net/publication/269076024_The_geology_of_the_Acropolis_Athens_Greece

The city grew slowly and became an important center during the Mycenean times (~1600-1100 BC) with a population of >10.000 people. While the city expanded, the Acropolis remained mainly a religious area. The foundations of buildings were buit using limestone from Piraeus (which was an island back then) and Aegina and for the big construction projects from late antiquity they brought marble from Penteli (very famous at that moment), limestones and conglomerates from Hymettos and probably from other places too. At this time Athens had an entire neighbourhood dedicated to masonry where people were carving everything from statues to temple columns. Piraeus island was connected with Athens and became its main acces route. Almost everything that was coming to Athens entered the city trough here from merchandise to food and from people to precious stones. And continues today!

Athens is yes another example of geology meeting archaeology, where geology can explain the natural processes behind the birth of a city and even of a nation. What would be history without the Acropolis?...