The Romans became famous not only for military campaigns. They were not bad engineers. That only are their graceful aqueducts, soaring in stone arches into the air. Many such structures have survived to this day. However, the Romans built the most unusual aqueduct at a depth of tens of meters underground. A "secret" super-water pipeline stretching from modern Syria to Jordan for almost a couple of hundred kilometers was discovered by German scientists.
The discovery was made by Professor Mathias Döring from the University of Applied Sciences Darmstadt (Hochschule Darmstadt), a specialist in fluid mechanics. The long abandoned and forgotten tunnel reminded of itself only in the oral traditions of local residents. Like, there is something mysterious underground, which is sometimes called the "channel of the pharaohs." It was said that gold was hidden in it, but no one really knew what was there in reality.
And so the expedition led by Döring dotted the i's. The mysterious structure is an underground Roman aqueduct built to supply water to the cities of the Decapolis.
In the Roman province of Syria (now the territory of Jordan), the area was arid, but Rome (being at the zenith of fame at that time) was not stingy with the idea that allowed to turn it into a blooming garden. It doesn't matter that the construction of this miracle of engineering took 120 years (from 90 to 210 AD). It really worked, and at the best of times, up to 700 liters of spring water per second was transported through a tunnel hidden in a mountainous area (this was shown by a large volume of mineral deposits on the walls)!
In total, construction crews, most likely made up of legionnaires, shoveled over 600,000 cubic meters of stone and earth, the equivalent of one quarter of the Great Pyramid. The scale was quite consistent with the heyday of the Roman Empire (photo by Mathias Döring).
Contrary to popular belief, Roman aqueducts did not necessarily pass over the land. Many of them combined aboveground and underground areas in one proportion or another.
It is not surprising: according to ancient Roman technology, the aqueduct should have had a very small and uniform slope along its entire length from the source to the point supplied with water. Therefore, engineers had to carefully consider the terrain on the route of their water supply system, invent tunnels to overcome hills and mountainous areas and spectacular bridges so familiar to many to overcome ravines, valleys and rivers.
Many aqueducts have been built in such a way that most of them pass underground. Even at a shallow depth (about a meter or, for example, five).
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This solved several issues at once: protecting the aqueduct from the effects of wind and rain, preventing its destruction during the war, and in the northern regions of the empire - and thermal insulation, which did not allow the aqueduct to freeze in winter.
Such, for example, is the Eifel aqueduct located near Cologne. It is one of the longest aqueducts in the Roman Empire. Its main part stretches for 95 kilometers (or rather, it stretched, since now only a few scattered sections remain from the grandiose structure).
The Eifel aqueduct owes its name to the mountains in which it originates. Water from several sources (each had its own small aqueduct to the main road) was carried by Eifel to the city of Colonia Claudia Ara Agrippinensium, now Cologne. Alas, there are not so many parts of this aqueduct (photos from wikimedia.org).
But the aqueduct that Döhring's team studied will easily compete with Eifel in terms of complexity and scale of work. And in terms of length, it is the record holder of the ancient world: its beginning and end are separated in a straight line by "only" more than fifty kilometers, but the total length of the conduit exceeds 170 km, of which 106 are in the underground part!
Moreover, the depth of the ancient aqueduct reaches up to 80 meters in some places. In fact, we have a tunnel of colossal complexity, punched through the rock. And here is a fundamental difference from the same Eifel. There, the depth of the concrete "pipe" (yes, it was just ancient concrete) is for the most part only a meter. The builders simply dug a trench along the pipeline route, erected an aqueduct in it and sprinkled it on top with soil. And what the Romans had to do in Syria cannot be called anything other than a feat.
The “source” of this aqueduct is located near the town of Dille, in the marshes, now dry and dry. The first 64 kilometers of the water conduit winds only along the surface (the remains of the structure can still be found). But then he successively dives into three tunnels, 1, 11 and 94 kilometers long. The end point of the ancient system is the city of Gadara, one of the pearls of ancient Palestine, a major trade center, one of the ten cities of the Decapolis, with 50,000 inhabitants. By the way, according to the Bible, it was here that Christ expelled demons from the possessed one and moved them into a herd of pigs.
But we got distracted. The construction of the Gadar aqueduct began under the Emperor Domitian. Rome literally bathed in the water supplied to the Eternal City by several aqueducts. And also bathed in luxury. Wealthy senators enjoyed spices from India and dressed in silks from China. Outlandish animals were brought to the capital and slaves were driven. And cities in the provinces also gradually became richer and more beautiful.
Döring was assisted by his students (photo by Mathias Döring).
At Gadar, Rome erected two theaters and intended to build a temple of nymphs with a large pool and fountains. Local water sources were already in short supply. It was then that they decided to lead an aqueduct to the city. A powerful underground source of life-giving moisture (now non-existent) was located near Dille. A concrete channel, closed from above, went from it (to prevent animals and birds, their excrement from entering the water, and also to prevent algae from developing in the darkness).
After the town of Adraa, problems began: the route was crossed by a mountain gorge. The conduit was turned and gradually lowered along the slopes, mainly biting into the thickness of the mountains, until it was possible to overcome this obstacle. The stone blocks of this part of the aqueduct can still be found at the bottom of the gorge.
But the biggest challenge was the creation of the longest continuous tunnel, which went already to the end of the phenomenal structure. First, it was necessary to carry out geodetic work of colossal accuracy, and then "stretch" the thread of the tunnel at great depths exactly under the "landmarks" that marked the route, moreover, carefully observing the accuracy of the slope. How did you manage it without modern tools?
After laying the route, engineers began drilling a huge series of auxiliary inclined shafts (with a slope of 50 degrees) along the entire future aqueduct. They walked every 20-200 meters of the track. The difference in height between the entrances was determined with colossal accuracy using measuring instruments and a giant chorobate level, borrowed by the Romans from the Persians. Further, the line was "lowered" along the steps of "service mines", which at the same time solved several problems at once.
The first is speed. With the sequential laying of the tunnel, only four legionnaires could work in it at the same time (the height of the tunnel is 2.5 meters, and the width is 1.5 meters). Punching 10 centimeters a day in the rock, they would have brought the aqueduct to Gadar only to our time. But in the mountains almost three thousand service tunnels were made (more than 600 of them have now been discovered by the Döring group), and now thousands of people could simultaneously build an underground aqueduct, making their way towards each other.
Construction scheme. 1 - auxiliary tunnels (mines) were supplied with steps and went into the rock for tens of meters; 2 - when the two sections approached the connection, the workers first punched small pilot tunnels, and after the bow they widened them; 3 - the legionnaires worked on two levels, arranged in a ledge, so that four of them could lead the tunnel from each side at once. The inset is a map of the aqueduct route showing the aboveground (4) and underground (5) parts (illustration Der Spiegel).
Of course, mistakes could not be avoided. There are bows in the tunnel, where you can see that in the last meters the workers began to perform zigzags, trying to catch the oncoming move. They were probably tapped and guided by sound.
And yet, the accuracy of the work is amazing: in the first 60 kilometers, the tunnel has a gradient of only 30 centimeters per kilometer!
The second problem, solved by thousands of mines, is tunnel ventilation during the work. The third is rock removal.
When Emperor Hadrian visited the Decapolis in 129, the construction was in full swing. The workers toiled day and night under the light of oil lamps and to the sound of the invocation of trumpets, and the lines of slaves lifted the stone cut with chisels up.
When the aqueduct was opened, it became a triumph of engineering. True, the triumph was overshadowed by a miscalculation. The level of the water coming from the tunnel was too low to feed the fountains promised once. Nevertheless, the water supply worked.
Now even finding him on the ground has proved to be a difficult task. Time has worked on a wonderful structure. In addition, almost all auxiliary mines along the aqueduct were walled up by the builders themselves - in order to protect the water from animal pollution.
Now, only a few entrances that look like holes in the ground are accessible to scientists armed with theodolites, climbing gear and GPS-navigators. But even these entrances are clogged with mountains of garbage and animal remains, so it turned out to be difficult to break into the depths.
Inside the tunnel, there is damp darkness, the flapping of bats' wings, mud and ancient walls on which letters appear. It is difficult to work here, scientists are often forced to go upstairs - there is not enough oxygen. The air is still. In some places, on the contrary, there are drafts that create a hum, like in a wind tunnel, and rainwater flows incessantly.
It was equally difficult and bit by bit to restore the picture of the construction of the water supply system. Still, Matthias's team intends to return to the Gadar Aqueduct in April to further explore this masterpiece of the Roman Empire.
Cross-section of mines and a tunnel in several places. Greek letters. Measurement scheme during construction. Several fragments of the tunnel and the remains of the aerial part of the aqueduct (photos from the site h-da.de).