YouTube is full of clips about Rome’s eleven aqueducts. Of course, the > 800 kilometers long water supply network that took centuries to build and delivered daily 1 cubic meter of water per person, still fascinates. It is one of Rome’s major engineering achievements. Building water pipes with a gentle decline of 5 per 1’000 meters cannot be done without mastering trigonometry. The Romans acquired the knowhow from Magna Graecia. Same is true for the techniques to build tall bridges or dig long tunnels.
The beautiful Roman Aqueduct in Segovia in Spain
Last summer we were looking for aqueducts in Magna Graecia. Unfortunately, we did not find any. They decayed or were swallowed by the alluvial plains. There are many aqueducts in the Aegean though, most of them of Greek origin but later refurbished and expanded by the Romans. The two most interesting ones are in Samos and Pergamon. There is also a prominent aqueduct in Constantinople. However it was built centuries later in 373 AD by Roman Emperor Valens to improve the water supply to his new capital. Winding through the hills north and west of Constantinople, it is a staggering 310 km long.
The Aqueduct of Constantinople is >300 km long and fetches Water from 100 km Distance
Aqueducts have multiple components. The magnificent bridges we see today are only part of it. For most of the distance, the water flows underground in 1 – 2 m deep channels. An aqueduct also include reservoirs, tunnels, siphons and cisterns. Usually, the channels followed the contours of the hills but, when necessary, more expensive solutions were built too. Aqueducts needed no pumps. They worked with gravity alone. The water gently flowed at a steady angle of 0.5 – 1.0 degrees.
Schematic Plan of a Roman Aqueduct with its main Components
Let’s have a look at the amazing Eupalinian Tunnel in Samos where we will be in week 3. The 1’036-meter-long tunnel was dug in the early 6th century BC to suppy fresh water to the island’s growing capital. It was named after Eupalios, an engineer from Megara (the town which founded Byzantion).
Inside the Eupalinian Tunnel which is finally open to Visitors
He used geometry to plan and execute the work. It allowed him to dig from both ends simultaneously. It was a first in history! For eight years, the miners chiseled daily 12 – 15 cm until both ends met. To increase the chance of the two tubes meeting, Eupalios bent their directions in the middle of the mountain. When eventually finished, the tunnel carried water for more than 1’000 years.
Plan of the First ever Tunnel built with Geometry
Centuries later, the Roman picked up his techniques and developed them further. The best example is the 170 km long aqueduct from the Syrian mountains to Gadara – a old Hellenistic town situated in northern Jordan, near the Israelian and Syrian border. Of its 170 kilometers of length, 94 kilometers are in tunnels. It was the longest tunnel system in antiquity. Rome occupied the town during the Jewish rebellion (70 AD) and garrisoned it permanently. Construction of the aqueduct started in 90 AD. It took 120 years to finish. The work was so important that two Roman Emperors visited. It remains an impressive piece of engineering.
The Gadara Aqueduct was built in small sections between 90 - 210 AD
Another Greek innovation was the use of siphons to cross a valley. Siphons are tubes that connect two bodies of liquid and allow the liquid to flow upwards, thus defying gravity. The system was probably invented by Egyptians who used it to transfer liquids between large jars. Later, Pythagoras from Samos, whom we encountered in Croton where he lived his last years, picked up this principle with the Pythagorean Cup. When the cup is filled beyond a certain level, the siphoning effect drains the entire cup. Designed to fight against greed and drunkenness, the principle of siphons found its first large scale application in the Aqueduct of Pergamon around 300 BC. We will visit the town at the end of week 1.
Supplying residential Pergamon with water was relatively easy and done by nine smaller aqueducts – channels deviating water from the surrounding rivers. Suppling the Acropolis which towered 335 meters above was a different matter. Pergamon’s Acropolis was a pilgrim site and housed temples for Zeus and Athene – the world famous Pergamon Altar now stands on the Museum Island in Berlin, though. It was sold by the Ottoman government to Germany in the 19th century and despite two world wars has survived completely intact - definitely worth visiting!
A Digital Reconstruction of the Acropolis of Pergamon with the famous Altar to the Right
To resolve the Acropolis’ water needs, a 40-kilometer-long aqueduct from the Madradag mountains was built. Important for our story are the last two kilometers where a 200-meter-deep valley had to be crossed. No bridge was tall enough. Even during Roman times, the maximum height of aqueducts was below 50 meters (Pont du Gard 49 m). The Coliseum is 57m tall. Taller structures cannot be built without having steel.
The Aqueduct of Pergamon with the famous Siphon - build around 300 BC
The Greek engineers solved the problem with a giant inverse siphon. About 2 km to the north of the Acropolis, the aqueduct emptied the water into a giant pool which was 35 meters higher than the Acropolis. The difference in altitude allowed the engineers to pressurize a lead pipe sufficiently (guess with 3.5 atmospheres) to make the water flow uphill to the Acropolis. There it flowed into a large cistern from where it was distributed further in small ceramic pipes. It is amazing how advanced Greek engineering was. Of course the Romans would copy it – they were masters in picking up good ideas and developing them further for their own use. Wonder how they dealt with lead poisoning. Both the Greek and the Romans knew that lead was poisonous. But this is for another blog.
The sophisticated Siphon of Aspendos which covered a Valley 1.67 km wide!
Could not find any technical drawings of the Pergamon’s siphon but found one from the Siphon of Aspendos. We visited the town which is famous for having the best-preserved Roman Theatre, in 2018. What makes Aspendos extraordinary is its elaborate siphon though. Built by Roman engineers in the 2nd century AD, it is another marvel of engineering. Large excavations and technical examinations were conducted in 2004. Today we understand fairly well how a Roman siphon worked.
View North from the Acropolis of Aspendos - both South and North Tower are clearly visible
Last but not least I shall devote some lines to Greek and Roman cisterns which were essential parts of the aqueduct systems. The supply of water is seasonal. The use of water fluctuates during the day with peak hours. Few people need water at night but everybody needs it for cleaning and washing after lunch and dinner. Cisterns were the vital buffers between supply and demand and had to be large. Luckily, Constantinople’s Roman cisterns survived. The new Ottoman rulers kept them in good shape and continued using them to supply water to Istanbul. The Basilica Cistern, the Theodosian Cistern and the Cistern of 1001 Columns are magnificent buildings which help us understand how important water management was for any ancient metropolis.
The magnificent Basilica Cistern in Istanbul is now open to Visitors
On our trip this summer we are thus going to visit three key elements of the Roman aqueduct system which we usually seldom see. The cisterns in Constantinople, the tunnel in Samos and the siphon in Pergamon. Greek engineering was just amazing, Chapeau!