Concrete in Rome

So I went to a public lecture at Melbourne Uni on Tuesday, called “From the Colosseum to the Baths of Diocletian: What Concrete can tell us about Social Change in Imperial Rome.” It was given by Lynne Lancaster of Ohio University. This was the first cool thing about the night: it was a woman, talking about concrete and stress points and vaulting ribs… very cool. The first funny thing was that it took two heads of departments (Classics, a bloke; Engineering, a woman [I think she was the head; I could have been wrong]) to turn some lights down so everyone in the audience – and there was a lot of people – could see the slides properly.

So, a number of things I found out are listed here. Lancaster has a book out at the moment, talking about some of these things; she made some joke about wantin a ‘sexier’ name, which I didn’t think was that sexier, but her publishers insisted that her title be searchable. So it’s really not sexy.

She started the lecture talking about factors affecting innovation, which I think she said she stole from someone else. Most of the rest of the lecture revolved around these issues, and how it affected concrete in Rome.
1. Accumulated knowledge
2. Evident need
3. Economic ability
4. Cultural/social/political acceptability

1. The accumulated knowledge required for buildings such as the Pantheon and other buildings of the early empire (her focus) was that of the arch (there’s evidence that there were arches from the 6th century BC – cool!), and use of pozzolana – volcanic ash used to reinforce the mortar.

2. Vaults got larger, which allowed for larger groups of people gathering together – which was convenient, since amphitheatres, theatres (numerous small vaults people sat on), and baths (fewer large vaults covering people) were becoming ever more popular.

3. Becoming an empire, rather than a good ol’ republic, brought different ways of collecting money for Rome – it also led to the wealth of one individual, or family, rivalling that of the state. And that wealth was often used on construction. The top builders, in her opinion, were Nero; Vaspasian; Trajan; Hadrian; Caracalla; Diocletian; and Constantine.

*Tangent-ish: the debasement of the coinage, which started under Nero. The denarius was about 97% silver under Augustis, but was only about 50% by the mid-third century. By this time, the coinage was so bad that the government wanted its taxes in kind, rather than money! This ended up having interesting repercussions for the building industry… see below…*

*Interesting tangent #2: When Trajan built his own little forum, he also modified Caesar’s – including a latrine. The cool thing about this is that the latrine was built on the second floor, meaning they had to use lots of arches to channel the weight. It also had nice windows….*

*And, just because: the Pantheon (I think Lancaster has a thing for the Pantheon…) has a 43m dome – the largest unsupported vault (I think I got that right), and two times larger than any previous dome: so interestingly, no incremental changes. It also has hollow, 6m wide walls, with extruded brick ribs…*

4. Brick industry development paralleled the increase in the use of vaults.
Under Trajan, politicians had to own land (I think I got that right – I might have missed something there). One way to profit from this was to sell clay, to make bricks. Brick use explodes from this time – it’s probably consequential. There’s evidence of bricks allowing for social advancement (slaves becoming freemen, etc). As well, there’s evidence that women owned and even produced bricks…. So in all of these ways there were incentives to Make Bricks.

**Break for a human demonstration of the necessity of ribs and vaults!**
Four women called up, to act as ribs – then Lancaster hung from their hands! and asked them where the tension was. And then, four men came up and put their hands on their shoulders – queue hanging again – and the women reported that there was less tension. Very, very cool.

Then there was scoria. It’s basically solidified volcanic foam, and was the only non-decorative stone imported into Rome, and it was used on imperial buildings. Most of the stuff that was used was from Pompey, but was brought after 79 – when the explosion from Vesuvius had covered the stuff – so it was hard to get to, but still they did it. Hello, lucre…

The Basilica Ulpia: why use columns, rather than a vaulted roof? Columns make the roof flat, and there was increasing interest in showing off colourful stone from captured territory. It also probably provided a very nice viewing platform for Trajan’s Column – so convenient!

Also at this time came the introduction of the use of window glass (from late in the first century). This led to huge changes in Roman perceptions of light and space, and raised expectations through the roof (tee hee). Buttresses become important for this development, and allows for baths to get bigger – good from a social and imperial point of view – and the light showed off the captured marble very, very nicely.

There were other bits and interesting pieces in the lecture – which I really enjoyed, if I haven’t mentioned that – but the last thing I wanted to mention related to that comment about taxes and debased coinage. Diocletian made a huge change by imposing a property tax on people living in Rome. The urban prefect, who was in charge of the area within a 100 mile radius of the city, used a form of barter to get building materials – and, on the other side, to reduce the taxpayer’s tax burden. Very, very clever.

Yay for public lectures! I love the Classics department at Melbourne!

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