Ostia

Isola Sacra – Existing Features

So the survey at the Isola Sacra has been running for the last three years. The area comprises an artificial island between Portus and Ostia Antica with the line of the Via Flavia running from north to south. A number of questions are being directed at the area, in particular relating to the location of the ancient coastline in the Roman period, the division and make-up of the ancient landscape an the presence or absence of buildings, workshop zones, cemeteries and other sites.

One thing that has stemmed from the survey to date is the presence of ancient canals sub-dividing the area, a small example of which appears below.

More of the same being processed at the moment suggesting the continuation of similar features. The area is marked by broad geological features also, all relating to the prograding of the Tiber delta in antiquity. For more information see www.portusproject.org/ and http://www.portusproject.org/fieldwork2007-9/regionalsurvey/results.html and http://bsr.academia.edu/StephenKay/Papers/185232/The_role_of_Integrated_Geophysical_Survey_methods_in_the_assessment_of_archaeological_landscapes_the_case_of_Portus.

Stock check

I should probably start by introducing myself – I’m Joe Williams, and I’m a PhD student.  I started my research about three months ago, at the University of Kent. My PhD is part of a larger project funded by the Leverhulme Trust, run by Drs Luke Lavan and Ellen Swift. This project is The Visualisation of the Late Antique City, and my contribution will be study of everyday urban artefact assemblages. If this project interests you, keep an eye on its website – at the moment all you’ll see is an “under construction” notice, but I’m gradually putting pages together in breaks from research so there should be more on there in the coming weeks.

Unfortunately for anyone who chooses to read this, the Day of Archaeology happens to correspond with my own “Day of Filing”, so there won’t be any news of fascinating ritual deposits, or any nice pictures (unless anyone really wants to look at a photo of a messy desk, in which case I’ll take one and send it to them). Earlier in the week I was helping out with organising and putting together an inventory of all the equipment stored in university buildings that belongs to the Late Antique Ostia field project, now in its fourth season; today I’m working at home doing a similar thing with the journal articles and other resources that I have on my computer (and as paper copies in folders, laptop bag, rucksacks, left in the printer and anywhere else you care to look). The main task of these first few months has been the literature review, so the hulking mass of things to read constantly threatens to overwhelm me! I’ve built up an extensive bibliography, organised thematically, but now I need to split most of it into two in order to keep works that present data and those that analyse data in separate parts of the essay – which will involve hundreds of quick checks, hence the filing.

The Institute of Classical Studies Library and the internet have been invaluable resources. So far it’s been a case of reading hundreds of abstracts, skim-reading tens of articles, and reading a select few articles in full, in order to have an overview of the relevant scholarship available. A lot of this has already been covered in the bibliographic essays included in Late Antique Archaeology volumes 3.2 and 5, so most of the work I’ve been looking at has been published since 2007. It’s incredible how much of this there is -if I could give one piece of advice to anyone about to start a research degree in September, it would be to pick a logical filing system as early as possible and stick to it! Endnote helps, but it has a few quirks so I find it helpful to arrange everything in such a way that I can find it without having to think up search terms that may or may not lead me to the right thing. Ideally this would be something I do on a daily basis, but of course it isn’t, so I need days like this once in a while to recover articles from the hiding places that seemed perfectly logical when I put them there. Speaking of which, I must get back to doing that.

Day of data processing – geophysical survey results from Isola Sacra

A day of processing of data, starting with the latest results from the geophysical survey at Isola Sacra, near Fiumicino, Italy.

 

 

This image shows a member of the survey team last year surveying using a fluxgate gradiometer over the central part of the landscape, an area of floodplain between the course of the river Tiber and the small Fossa Traiana, which demarcates the Isola Sacra between Portus and Ostia Antica. So far some 120 hectares of data have been collected, and the latest stage of processing is under way. More to follow later.

Ancient concrete? Really?

Yes, really.  I first fell in love with old buildings in Pompeii, where I spent summers working as an excavator from 2002-2008. Every day it struck me that I was in a place that still looked and felt like a real city. To my mind, this was down to the fact that the buildings are still standing. After more than 2000 years. Someone did something very, very right when making those buildings and I want to know more.

For my D.Phil research, I have landed in an opportunity to study structures in Ostia, Italy, which is also a preserved city-sized site.  The structures I’m investigating are all brick and mortar masonry, with concrete filling up the center wall core. This is what Vitruvius called opus caementicium. To be honest, I’m most interested in the people who made it: the builders who developed this wonderful, magical material that is still performing successfully more than 2000 years after it was first installed. Where did they get their materials? Why were certain materials preferred over others? How were the materials processed and mixed together? How did builders’ choices affect the concrete and its performance? Were the same mix types used for both public and private structures? Why is this stuff still standing? These are the questions driving my research, and I am looking to answer them by investigating the material itself.

To give a quick overview, the mortar and concrete I am analyzing was made of lime, volcanic sand aggregate, and water. Sounds rather simple, however, the combination of materials they were using produced complex chemical reactions, known to modern concrete scientists as pozzolanic reactions, which resulted in a sophisticated, high quality material. My sample collection was collected from a series of structures in Ostia from the 2nd century CE, by which time – at least in Rome – concrete was well-developed and had been employed in large-scale Imperial building projects. My task now is to analyze the Ostian structures to determine how well-developed their concrete industry had become by that time. The benefit of a site like Ostia is that the ancient city is left largely in tact without modern development. This means that unlike in Rome, where centuries of modern development has destroyed all but the most protected monumental structures, it will be possible to evaluate the buildings within their original cultural context.

The analytical techniques employed for my research are borrowed from geology and concrete science, which makes this a truly interdisciplinary project. My samples are essentially synthetic composites of natural materials that can be investigated with traditional petrography. I’m using light microscopy of thin sections to identify and quantify the aggregate, to describe the cementitious matrix, and to identify any  obvious degradation features or alteration products. Today I’m working on point counting one of the samples, which is pretty straight forward. I move across the sample in 1 mm steps, and at each location I record what I see in the cross hairs of the eyepiece. Besides the obvious benefit of quantifying each of the different components, I’m also getting to the know the sample really well. As I go, I’m recording information about the state of degradation or alteration, the shape and fillings of any cracks or holes, particle size and shape, and any other details that may give me a clue about what the builders were doing when they made the concrete.

I am also using scanning electron microscopy (SEM) to collect high-resolution, high-magnification backscatter images of the samples. At this scale I can get a better look at the binder-aggregate interface to see how well-bonded these components are. It is also possible to see any microscopic cements that have formed in pores, cracks, and the vesicles of aggregate clasts that would otherwise not be visible. The SEM also detects the atomic weights of everything in the sample, which show up as differences in the greyscale colour of the image. It  also can calculate the chemical composition of the different components, so using a combination of chemical data and backscatter images, I can determine what types of cements have formed (strengthening) and how much leaching has occurred across the matrix (degradation). The ratio of calcium to silica is key in both cases.

X-ray diffraction is also on the menu, assuming I can find the funding to pay for it. This technique is incredibly useful for identifying the mineral assemblage in rocks and materials. In this case, I will use it to confirm the original petrographic identification of minerals in the aggregate and to find any other alteration minerals that could not be seen in thin section. The presence of certain minerals like gypsum or ettringite usually indicate alteration of the mortar itself, but minerals such as stratlingite and calcium-aluminum-silicate-hydrates suggest the mortar was rather well-formed in the first place.

So today, I’ll be giving an account of what it’s like for me in the lab. I realize that being stuck in the lab sounds like a death sentence to some people, but for me, it’s where the magic happens.