Babylon, even phonetics of the name, has a great capacity for suggestions, even now, the area stricken by war and ongoing violence. So it must also occur in antiquity.
Some works of the Ancients impress us by its dimensions and other for their beauty. The best examples are the "seven wonders of the ancient world," including "the Hanging Gardens of Babylon." There is another work in Babylon, in addition to the gardens, less known, but no less impressive: the construction of a tunnel under the River Euphrates which linked secretly the existing royal palaces on either side of the river.
Before developing the theme, we should remember that Babylon was on the Euphrates in land what is now Iraq. Its ruins were partially rebuilt by Saddam Hussein in the twentieth century and they are located about 110 kms. from Baghdad in Babil province, opposite the town of Hillah.
This area is rich in bitumen and petroleum, as it is well known, also in antiquity. But maybe not all readers know that the bitumen or asphalt, which then surfaced in the same area where today the oil is extracted, was used in the construction of buildings among other things, as the Roman architect Vitruvius tells us .
Vitruvius: De Architectura libri decem (De Architectura): I, 5,8 (39)
With regard to the material of which the actual wall should be constructed or finished, there can be no definite prescription, because we cannot obtain in all places the supplies that we desire. Dimension stone, flint, rubble, burnt or unburnt brick,—use them as you find them. For it is not every neighbourhood or particular locality that can have a wall built of burnt brick like that at Babylon, where there was plenty of asphalt to take the place of lime and sand, and yet possibly each may be provided with materials of equal usefulness so that out of them a faultless wall may be built to last forever. (English translation by Morris Hicky Morgan, 1914))
De ipso autem muro, e qua materia struatur aut perficiatur, ideo non est praefiniendum, quod in omnibus locis, quas optamus copias, eas non possumus habere. sed ubi sunt saxa quadrata sive silex seu caementum aut coctus later sive crudus, his erit utendum. non enim, uti Babylone abundantes liquido bitumine pro calce et harena ex cocto latere factum habent murum, sic item possunt omnes regiones seu locorum proprietates habere tantas eiusdem generis utilitates, uti ex his comparationibus ad aeternitatem perfectus habeatur sine vitio murus.
And again Vitruvius: Book VIII cap. 3, 8:
In Babylon, a lake of very great extent, called Lake Asphaltitis, has liquid asphalt swimming on its surface, with which asphalt and with burnt brick Semiramis built the wall surrounding Babylon. At Jaffa in Syria and among the Nomads in Arabia, are lakes of enormous size that yield very large masses of asphalt, which are carried off by the inhabitants thereabouts. (English (Morris Hicky Morgan, 1914))
Babylone lacus amplissima magnitudine, qui λίμνη ἀσφάλτιτις appellatur, habet supra natans liquidum bitumen; quo bitumine et latere testaceo structum murum Samiramis circumdedit Babyloni. item Iope in Syria Arabiaque Nomadum lacus sunt inmani magnitudine, qui emittunt bituminis maximas moles, quas diripiunt qui habitant circa.
Small digression: it is very known in the ancient world that the walls of Babylon were made with fired brick is something very present in the ancient world; by way of example I cite that the satirical Roman poet Juvenal, who lived in the second half of the first century and the first of II AD, refers to it in connection with the entry of Alexander the Great in Babylon sick unto death. He says in Satire 10, 169 et seq.
One globe is all too little for the youth of Pella; he chafes uneasily within the narrow limits of the world, as though he were cooped up within the rocks of Gyara or the diminutive Seriphos; but yet when once he shall have entered the city fortified by the potter's art, a sarcophagus will suffice him! Death alone proclaims how small are our poor human bodies! ([Translated by G. G. Ramsay])
Unus Pellaeo iuveni non sufficit orbis;
aestuat infelix angusto limite mundi
170ut Gyarae clausus scopulis parvaque Seripho;
cum tamen a figulis munitam intraverit urbem,
sarcophago contentus erit. mors sola fatetur
quantula sint hominum corpuscula.
Pliny refers extensively to the asphalt or bitumen; at another time I will comment it. On the subject that interests us, he tells us in Natural History, 35, 51.5
It has been used, too, as a substitute for lime; the walls of Babylon, for instance, which are cemented with it. (Translation by John Bostock, M.D., F.R.S. H.T. Riley, Esq., B.A. London. 1855)
calcis quoque usum praebuit ita feruminatis Babylonis muris.
Well, Philostratus of Athens (160 / 70-249) wrote an interesting biography of Apollonius of Tyana, which is more like a novel, or rather he wrote a novel that seems a biography. In this work information and certain details are mixed with elements of the unbridled fantasy in harmony. Apollonius decided to travel to India and went through Babylon, describing it in some detail.
Philostratus of Athens, Life of Apollonius of Tyana, book I,25:
I FOUND the following to be an account of the sage's stay in Babylon, and of all we need to know about Babylon. The fortifications of Babylon extend 480 stadia and form a complete circle, and its wall is three half plethrons high, but less than a plethron in breadth. And it is cut asunder by the river Euphrates, into halves of similar shape; and there passes underneath the river an extraordinary bridge which joins together by an unseen passage the palaces on either bank. For it is said that a woman, Medea, was formerly queen of those parts, who spanned the river underneath in a manner in which no river was ever bridged before; for she got stones, it is said, and copper and pitch and all that men have discovered for use in masonry under water, and she piled these up along the banks of the river. Then she diverted the stream into lakes; and as soon as the river was dry, she dug down two fathoms, and made a hollow tunnel, which she caused to debouch into the palaces on either bank like a subterranean grotto; and she roofed it on a level with the bed of the stream. The foundations were thus made stable, and also the walls of the tunnel; but as the pitch required water in order to set as hard as stone, the Euphrates was let in again on the roof while still soft, and so the junction stood solid. (Translation by F.C Conybeare, 1912)
Note: A plethrons is equivalent to 29.6 m. These measures of perimeter and thickness are very close to these of Herodotus, I, 178: 480 stadia for the perimeter and 50 royal cubits (about 25 m) thick, but the height that Herodotus gives, 200 royal cubits (about 100 m ) is more than twice this one of Philostratus.
Herodotus tells us on I, 178- 179:
When Cyrus had made all the mainland submit to him, he attacked the Assyrians. In Assyria there are many other great cities, but the most famous and the strongest was Babylon, where the royal dwelling had been established after the destruction of Ninus (Ninnive). Babylon was a city such as I will now describe. It lies in a great plain, and is in shape a square, each side fifteen miles in length; thus sixty miles make the complete circuit of the city. Such is the size of the city of Babylon; and it was planned like no other city of which we know. Around it runs first a moat deep and wide and full of water, and then a wall eighty three feet thick and three hundred thirty three feet high. The royal measure is greater by three fingers' breadth than the common measure.
Further, I must relate where the earth was used as it was dug from the moat and how the wall was constructed. As they dug the moat, they made bricks of the earth which was carried out of the place they dug, and when they had moulded bricks enough, they baked them in ovens; then using hot bitumen for cement and interposing layers of wattled reeds at every thirtieth course of bricks, they built first the border of the moat and then the wall itself in the same fashion. On the top, along the edges of the wall, they built houses of a single room, facing each other, with space enough between to drive a four-horse chariot. There are a hundred gates in the circuit of the wall, all of bronze, with posts and lintels of the same. There is another city, called Is,1 eight days' journey from Babylon, where there is a little river, also named Is, a tributary of the Euphrates river; from the source of this river Is, many lumps of bitumen rise with the water; and from there the bitumen was brought for the wall of Babylon. (English translation by A. D. Godley. Cambridge. Harvard University Press. 1920.)
Herodotus goes on to describe the city and the impressive refurbishment which I will comment on at another time. But I want to reproduce what he tells us in chapter 186 which is a significant variation in what Philostratus told us, but they are not necessary two contradictory version but opposed; after all, if the tunnels were secret, they did not must to be known by all of the world:
So she made the deep river her protection; and this work led to another which she added to it. Her city was divided into two parts by the river that flowed through the middle. In the days of the former rulers, when one wanted to go from one part to the other, one had to cross in a boat; and this, I suppose, was a nuisance. But the queen also provided for this; she made another monument of her reign out of this same work when the digging of the basin of the lake was done.
She had very long blocks of stone cut; and when these were ready and the place was dug, she turned the course of the river into it, and while it was filling, the former channel now being dry, she bricked the borders of the river in the city and the descent from the gate leading down to the river with baked bricks, like those of the wall; and near the middle of the city she built a bridge with the stones that had been dug up, binding them together with iron and lead.
Each morning, she laid square-hewn logs across it, on which the Babylonians crossed; but these logs were removed at night, lest folk always be crossing over and stealing from one another.
Then, when the basin she had made for a lake was filled by the river and the bridge was finished, Nitocris brought the Euphrates back to its former channel out of the lake; thus she had served her purpose, as she thought, by making a swamp of the basin, and her citizens had a bridge made for them. (English translation by A. D. Godley. Cambridge. Harvard University Press. 1920).
Strabo, who lived between 64 and 63. C. and 19 or 24 d. C., has also given us an interesting description of Babylon in Book 16, 2
….His wife, who succeeded her husband, and founded Babylon, was Semiramis. These sovereigns were masters of Asia. Many other works of Semiramis, besides those at Babylon, are extant in almost every part of this continent, as, for example, artificial mounds, which are called mounds of Semiramis, and walls7 and fortresses, with subterraneous passages; cisterns for water; roads8 to facilitate the ascent of mountains; canals communicating with rivers and lakes; roads and bridges. (The Geography of Strabo. Literally translated, with notes, in three volumes. London. George Bell & Sons. 1903.)
And soon after, he makes us a complete description of Babylon, that I reproduce partly, in the Book 16, chap. 5:
Babylon itself also is situated in a plain. The wall is 38518 stadia in circumference, and 32 feet in thickness. The height of the space between the towers is 50, and of the towers 60 cubits. The roadway upon the walls will allow chariots with four horses when they meet to pass each other with ease. Whence, among the seven wonders of the world, are reckoned this wall and the hanging garden: the shape of the garden is a square, and each side of it measures four plethra. It consists of vaulted terraces, raised one above another, and resting upon cube-shaped pillars. These are hollow and filled with earth to allow trees of the largest size to be planted. The pillars, the vaults, and the terraces are constructed of baked brick and asphalt.
The ascent to the highest story is by stairs, and at their side are water engines, by means of which persons, appointed expressly for the purpose, are continually employed in raising water from the Euphrates into the garden. For the river, which is a stadium in breadth, flows through the middle of the city, and the garden is on the side of the river. The tomb also of Belus is there. At present it is in ruins, having been demolished, as it is said, by Xerxes. It was a quadrangular pyramid of baked brick, a stadium in height, and each of the sides a stadium in length. Alexander intended to repair it. It was a great undertaking, and required a long time for its completion (for ten thousand men were occupied two months in clearing away the mound of earth), so that he was not able to execute what he had attempted, before disease hurried him rapidly to his end. None of the persons who succeeded him attended to this undertaking; other works also were neglected, and the city was dilapidated, partly by the Persians, partly by time, and, through the indifference of the Macedonians to things of this kind, particularly after Seleucus Nicator had fortified Seleucia on the Tigris near Babylon, at the distance of about 300 stadia. Both this prince and all his successors directed their care to that city, and transferred to it the seat of empire. At present it is larger than Babylon; the other is in great part deserted, so that no one would hesitate to apply to it what one of the comic writers said of Megalopolitæ in Arcadia, “‘The great city is a great desert.’” (The Geography of Strabo. Literally translated, with notes, in three volumes. London. George Bell & Sons. 1903.)
All of this certainly impresses us, but especially the ingenuity to build a waterproof tunnel under the river. Indeed, this technique of tunneling opencast is still used today where it is easier than underground drilling. Similarly it is used for waterproofing terraces and roofs of buildings the called "roofing felt", which is nothing but a modern version of the ancient Mesopotamian bitumen or asphalt.