History and Aqueducts Generally
Aqueducts transport water for public fountains around the city, public baths like the Baths of Caracalla, or to create artificial lakes to stage sea battles, and there were of course many other uses. The aqueducts were a very important and impressive feat of Roman infrastructure and allowed for a great density of population within the city and for a level of sanitation that was well beyond that of other societies at the time. These aqueducts were basically long channels that started in the mountains dug into an aquifer and then dug through hillsides and rested upon large arches or arcades to maintain a low radiance or angle until it reached the city of Rome.
In 144-140BC, praetor Q. Marcius built the Aqua Marcia, or at least headed the project and design. It spanned about 91.7km or ?mi. and served 1102.5q (quinariea) or about 190,000m3 per day. Its purpose: to transport water to the people of Rome, this aqueduct was “72% … personal use, either private individuals or to the general public”(Weston). The Marcia was known for having good quality water. On top of the Aqua Marcia were built two other similar aqueducts, the Aqua Tepula and the Aqua Julia, at least for some amount of stretch of their journeys.
Censors Ganaeus Servilius Caepio and Lucius Cassius Longinus finished the Aqua Tepula in 125BC after starting a year earlier. It stretched about 22km or ?mi. Its name, Tepula, comes from its water being tepid or warm and because of this “it may have been intended for industrial purposes only”(Weston). Where as the Marcia was known for having good quality water for drinking, the Tepula was not. It had a low public use of about 50q or ?per day, but a high public use of about 237q of a total of 331q or 17,800m3 per day which was a much lower value than many of the ancient aqueducts. “Although it entered the city at a high enough level for widespread distribution, its limited capacity and poor quality precluded this”(Weston).
In 33BC Marcus Agrippa built the Aqua Julia traveling “from new springs near the source of the Tepula in the Alban Hills 22.9 km [or ?mi] into the city”(Weston). Almost half of it (10.4km) was above group, and the rest underground. As the Tepula did, the Julia traveled on top of the Aqua Marcia making it a three high aqueduct at least in places. It’s not for certain weather it was entirely so, for less is known about the route of the Tepula, but in the picture below you can see the stack of three aqueducts. The Julia was mostly intended for Public uses supplying 383q or ?per day of 597 or 48,000m3 per day; about a quarter of the Maria. Since it had a higher elevation than both the Tepula and the Marcia, it was able to serve many more regions of the city, but it was believed that the Julia was “specifically planned to meet the water needs of Augustus’ building program in the central and eastern districts of the city”(Weston).
Path and Source
“The source of the Marcia “was a series of springs on the right bank of the upper Anio just below Agosta on the road to Subiaco, in the same area where numerous spring houses gather water today for the ancient aqueduct’s modern counterpart, the Acqua Marcia Pia” (Aicher 36)
The beginning of the Marcia’s journey lies mostly underground and it follows along the banks of the Tiber River. It starts on the rivers right bank for about 10km and the crosses to the other bank of the Tiber. About another 10km from there, the Marcia strays from the bank of the Tiber and goes underground until about the last 10km in which it comes from the ground to finish the route on arches and substructures.
The Aqua Tepula collects its water from the north slopes of the Alban Hills. “It’s source was a number of rivulets in the Marciana valley, 2km. west of Grottaferrata” (Aicher 38). The Tepula ran above the channel of the Marcia a few km. before the Marcia rose to the surface. The Tepula only ran about 5km. independent of the Marcia. In 33BC, the Tepula was abandoned and its water source mixed with that of the Aqua Julia’s.
The Julia was “only a few kilometers upstream of the Tepula’s, just southeast of Grottaferrata and below the roads to Marino and Rocca di Papa” (Aicher 38). As stated earlier, the Tepula’s water was added to that of the Julia’s when they intersected just a few kilometers before both intersecting with the Marcia.
So for much of the span of the Tepula and the Julia they were stacked with the Marcia. They could have done all three aqueducts right beside each other, but they chose to put them one on top of the other. It is important to ask why they did this? The Romans didn’t do things without reason, especially large undertakings like the building of an aqueduct. The answer is quite simple however. To use the path of a previously made aqueduct and just build on top saves a lot of time, labor, and material. This way they aren’t really making entirely new arcades, which take a lot of work, and I’m sure was a massive expenditure to Rome. Also, by using the previously made arcades and pathways, it took less calculation to make sure that the gradient was correct.
Gradients and Tools of the Aqueducts
If the aqueducts were running all the way from the mountains at a greater height than that of the city, then why didn’t the Romans just dig a channel from Rome to the side of a mountain and then dig in? Ancient Rome is famous for what sort of infrastructure they were able to create with the time they were in, and they weren’t just making guesses; they knew what they were doing. The mountains were most of the time not that close to Rome and definitely not a landscape that was a flat, straight shot from water sources out of Rome into Rome. They had to have the water coming in at a gradients or slope such that it could travel in a straight line (or at least close to a straight line) the entire way. This required for much of the aqueducts they built to be mostly underground only coming up when getting close to the city; and very careful planning of when that would happen and how high that water would come into the city. So, what first needed to be done when creating an aqueduct was to plan the line.
The general greatest gradient you could have was 3m per km, which is the same as 0.3% gradient. So the goal was to get under this value, or there could be repercussions. With values too high for the slope or the gradients, you could have the water coming in too quickly to the city that the volume of input is greater than the use, so you could have overflow (however most overflow was planned to go into the river anyways). Another problem you would run into is with higher gradients is that the volume of the water in the aqueduct channel may become too great; with this and the speed of the water you could start breaking down the channel itself. A very famous aqueduct, the Pont du Gard only drops 0.67m per km; a gradients of 0.067%. This is very impressive and because of this the water did not break down the channel very much, so it remains in fairly good shape today. However, it had a rather low output because of this gradient, so there is a happy median to be found when constructing an aqueduct.
To plan the line the Romans used a number of tools that they had fashioned that were much like levels. The first tool however was not. And that was the T-board.
“The T-board is a simple measuring device for which no ancient evidence, archaeological, literary or other, exists, and which is postulated because something like it is needed for establishing the repeated or projected gradient” (Hodge 197).
It is basically a wooden stake in the shape of a T with the bottom of the T being the stake. “It’s purpose is simply to reproduce and project downhill the sloping line of an already calculated gradient” (Hodge 197). It is used in a group of three with an individual operating each one. Basically they align the three T-boards at the desired gradients to create the path, and once those are aligned they leap frog the T-boards and move forward. They continue to do this until they go down to where the source feeds.
Another tool that they used when creating the line was the chorobates. This one was much like a level. It was very important to early leveling and establishing gradients. “Essentially it is nothing more than a long trough of some kind that can be filled with water, thereby giving a level surface across which distant objects can be aligned” (Hodge 199). The first picture below is an example of what a primitive one may look like, but for more accuracy much longer ones were used like in the second picture below. The larger more common chorobates were narrow, 20 to 30 ft. long, and you could take a sighting across it to see what point it was level with. This use of a sighting was believed to be used with a sort of sighting rod with some sort of target to see, but there are no archaeological remains of one, rather some writing found on them though to give us an interpretation as shown in the picture below. The chorobates also had plumb lines hung from the corners, which were also used for leveling, however they were not nearly as effective as the water trough aspect of the device. The last picture below demonstrates how they used it between a previously measure gradients of point A and B.
Next, we have the dioptra. Hodge has a good description of the dioptra so I will allow him to speak of it:
“It is essentiall a flat disc mounted on top of a pedestal or tripod and can be tilted in the vertical plane as well as rotated horizontally. By means of two sights mounted a diametrically opposite points on the rim, the alignment and relative angles of distant points can be read off; the tilt and rotation are imparted by a pair of worm-and mesh screws, which are calibrated so as to record the number of turns given” (Hodge 202).
The dioptra was believed to not be as commonly used as the chorobates because it was expensive; extravagant. On top of that, it was believed to not be as accurate as the chorobates either. However, it was versatile; very easy to move in comparison. The dioptra was also used by astronomers as well.
The last tool that I will cover is the groma. It was a fairly simple tool in appearance and use. The groma consisted of two perpendicular pieces in the shape of an X mounted flat on top of a pole with a plumbline hanging from each end of the X. Each length of the X could be used as a sight to check straight lines. And when used both ways it acted as a tool for determining right angles. It was mainly used to determine property lines and its use on aqueducts was limited however it benefited the survey process. Of these three tools I have described, the groma was probably used the least in the making of an aqueduct.
Aqueduct as a Structure
There were three different types of channels or tubes through which water was funneled in aqueducts. There are masonry channels, lead pipes and terracotta pipes. Most of the length of aqueducts was usually masonry channels, and slightly subterranean. They were “usually some 50cm to 1m below ground” (Hodge 93) as shown in the picture below. Most of these only slightly subterranean aqueducts were less of tunneling projects, and more of excavations where the conduits were built, and then covered with soil. The Marcia was generally a masonry channel. The cross-section of it varied over its length, but it was generally 0.90m wide by 2.40m. Every now and then however, the roof was flat and sometimes pointed. An example of a pointed roof from the Aqua Claudia is shown below. The water level in these structures was usually not that high, usually half to two-thirds full, however in the Claudia was much lower as you can see in the image. The reason they chose for them to have a height much greater than the water level was to allow access for people to come in for cleaning and maintenance.
To create the material used for these masonry channels the Romans would mix quicklime, sometimes broken pots, and “either sand or crushed brick, looking yellowish or reddish in color depending on which is used” (Hodge 98). To get quicklime you basically need to just burn limestone. This mixture is known as stucco. Then they would apply this to the channel given a skeleton of plywood or boards. A picture of this is shown below where you can see the board’s outlines in the cement of the Aqua Claudia. The Romans would lay several layers of this composition and usually let it sit for a good amount of time, somewhere around three months per layer (Hodge 98).
After this the floors and walls of the cement masonry channels were made to be waterproof. They did this by polishing the cement making it smooth so that calcium carbonate would not build up as much, and so that the surface would have less friction allowing water to move down the channel more easily. Also, “this hardens the top layer, which thus acts as a protective skin for those below it” (98).
Beginning of the Aqueduct
- First cover the history and the purpose. Be more general at first talking less about the MTJ and more about aqueducts.
- Talk about the path of the MTJ and find a map of its route if possible. Maybe try to find the reason for its path; nothing is done without reason. Then after that talk about why they had three layers rather than three rows
- Talk about how much of it is above ground as apposed to under ground and why that is. Then from here based off the explanation you should be able to more forward and talk about the gradience and how they go about leveling it out (tools). Briefly talk about the groma, dioptra, chorobates theodolite and anything else that is applicable.
- Now begin examining it as a structure talking about material it was made out of on the inside and outside. (Building tools maybe).
- Start to examine the end that goes into the aquifer and talk about how they get the water going in there if possible. Also this would be a good time to talk about how they did tunneling with many wells. A picture would be good here.
- Now you could begin to talk about the structure with water. How much water would flow through it, the water level, what was in the water, general uses in the city of Rome and the specific uses of the MTJ.
- Talk about possible health issues that could result from aqueducts in general and weather or not this applies to the MTJ.
- Give a good briefing on inspection, maintenance and regulation of aqueducts in general and the MTJ if possible. Talk about the dimensions of the inside and how it made it so that people could enter to do fixes and such. Also how they would divert the water from one aqueduct to another when they needed to do a cleanup. Use the picture from the Aqua Claudia here. On top of that bring up calcium carbonate and how it as a hard water created build up.
- Talk about its decline in use; its fall. And what happened to bring about its demise.
- Finish off with the MTJ today and how it is still standing in places and the park it is in.