One of the things that occurred to me today as I was working on the new wall we are building is the fact that we are participating in an activity that humans have been pursuing for quite some time.
Concrete has been in use since Roman times. Many of the buildings that still exist in Rome were built using concrete. The Romans had not discovered using metal reinforcing in their concrete structures, but they used aggregate and rubble and cement to build their roads and the aqueducts. Some places on the web claim that the secret of making concrete was lost for many centuries and was not rediscovered until a British engineer rediscovered it in 1756. Frankly, I’m not buying this story because if you look around Europe you can see plenty of evidence of cement being used in the interim.
For example, in Ronda, Spain, the Puente Viejo (Old Bridge) was built in 1616, and it clearly shows evidence of being made using very similar construction techniques as Jim and I are using today.
Additionally, in Lisbon the Castelo de Sao Jorge has slip form construction all over.
This hill was initially fortified by the Romans, followed by the Visigoths and then the Moors. In 1147, the first king of Portugal, Alfonso Henriques, captured the castle and it was used as the royal palace for several centuries. I’m not sure exactly who built the walls in the next photos, or when, but it is obvious that cement was being utilized. Additionally, these arrow slits show that the builders were happy to use any material that was hauled up the hill to the building site.
This wall is a great example of the opportunistic use of materials in castle construction. Notice that they didn’t always bother to use worked stone for their walls, but when it was available it was used to good advantage. In the following picture you can see how the builders made the outside corner of the castle wall using the worked stone they had available. The rest of the wall has whatever rock they came across.
Our wall continues to grow nicely, and we have gotten better at the technique.
This whole exercise is sort of like going to the gym and doing squats for a few hours at the same time you are lifting light weights for many many reps. The difference is that when you are done with this kind of workout, you have something concrete to look at.
the havens 