And now a little bit of history.
The excavated remains of a Roman town at Tharros, Sardinia.
The layout of the town can be clearly seen
and the buildings both private and public can be identified.
From places like this we can start to get a picture
of the lives of the people that walked these streets 2,000 years ago.
And in Italy, the centre of the Roman empire,
it's possible to pick out other remains of Roman life.
The granite quarries of Santa Teresa
were used between the second and fourth century AD
and they were probably the property of an Olympian household.
Once you get your eye in, there is evidence of the workings all about.
There are half-finished columns
intended for buildings all over the place.
Running out into the sea are the remains of a Roman quay
where the boats loaded up the prepared columns and blocks.
In the living rock are chisel marks where blocks were being worked on.
At that time, the blocks and above all the columns,
were exported using large cargo ships.
Without doubt columns from Santa Teresa were exported to Rome
where they can still be seen in archaeological sites.
There are probably others in other archaeological areas
but we need to investigate these further.
How do they know where the columns and blocks from here
have ended up?
The clue is in the rock itself.
It's granite.
There are three elements of the granite -
uranium, potassium and thorium - which are naturally radioactive.
They emit gamma rays and every granite is different.
They are all of different ages
and have different amounts of these three elements in them.
They give a chemical fingerprint that can be matched up
with any granite artefact you come across.
And they turn up in some unlikely places.
Windsor Park, England.
The ruins from the Roman town of Leptis Magna in North Africa
found their way to England in the 19th century.
Olwen Williams-Thorpe wants to know where these granite columns
originally came from.
She's looking for their chemical fingerprint
with a gamma ray spectrometer.
This white object is what we call the probe,
part of the gamma ray spectrometer.
That's a machine designed to measure gamma rays.
Inside that probe is a crystal.
The crystal is made of mostly sodium
and how it works is that gamma rays are zapping into it.
When they enter the crystal they produce tiny flashes of light
and all that we're doing is counting the number of flashes of light
and we're measuring the intensity of each flash of light
and that tells us how many gamma rays we're looking at or detecting
and what elements the gamma rays are coming from.
Stored in the machine is the uranium/potassium/thorium signature
for these columns.
All she has to do now is match it up with what she already knows
of quarry sites in the Mediterranean.
It's a typical signature of a granite which comes from a quarry
in the north west of Turkey, in an area called the Troad.
So those three elements tell me that that column is very likely
to come from that particular quarry
where we know the Romans were quarrying, producing columns.
We've got columns left at some of their quarrying sites
and the chemistry matches up the column and the quarry.
They match very precisely and so we can be fairly sure that
that column comes from north west Turkey.
What does this tell us?
How does chemistry help our understanding of the Romans?
What it tells us is something about the level of sophistication
in trade and movement of goods in the ancient world.
What we've got here, is in the Roman Mediterranean area
we've got huge granite quarries
being exploited between the first and fourth centuries AD,
massive amounts of granite being taken away to make columns.
They're being shipped across the Mediterranean
literally thousands of kilometres.
The level of sophistication that the Romans reached
was really not equalled in Europe until the industrial period.
