The Gardens were purportedly built in the ancient City-state of Babylon, near present-day Al Hillah, Babil province, in Iraq.
The Hanging Gardens were not the only World Wonder in Babylon; the City walls and obelisk attributed to Queen Semiramis were also featured in ancient lists of Wonders. The gardens were attributed to the Neo-Babylonian King Nebuchadnezzer II, who ruled between 605 and 562 BC. He is reported to have constructed the gardens to please his homesick wife Amytis of Media, who longed for the plants of her homeland. The gardens were said to have been destroyed by several earthquakes after the 2nd century BC. The Hanging Gardens of Babylon are documented by ancient Greek and Roman writers, including Strabo, Diodorus Siculus and Quintus Curtius Rufus. However no cuneiform texts describing the Hanging Gardens are extant, and no definitive archaeological evidence concerning their whereabouts has been found.
Ancient writers describe the possible use of an Archimedes screw like process to irrigate the terraced gardens. Estimates based on descriptions of the gardens in ancient sources say the Hanging Gardens would have required a minimum amount of 8,200 gallons (37,000 litres) of water per day. Nebuchadnezzar II is reported to have used massive slabs of stone, a technique not otherwise attested in Babylon, to prevent the water from eroding the ground.
In ancient writings the Hanging Gardens of Babylon were first described by Berossus, a Babylonian priest of Marduk who lived in the late 4th century BC, although his books are known only from quotations by later authors (e.g., Flavius Josephus). There are five principal writers (including Berossus) whose descriptions of Babylon are extant in some form today. These writers concern themselves with the size of the Hanging Gardens, why and how they were built, and how the gardens were irrigated.
Josephus (c. 37–100 AD) quoted Berossus (writing c. 280 BC), when he described the gardens. Berossus described the reign of Nebuchadnezzar II, the King he credits with the construction of the Hanging Gardens.
“In this palace he erected very high walks, supported by stone pillars; and by planting what was called a pensile paradise, and replenishing it with all sorts of trees, he rendered the prospect an exact resemblance of a mountainous country. This he did to gratify his queen, because she had been brought up in Media, and was fond of a mountainous situation.”
Diodorus Siculus (active c. 60–30 BC) seems to have consulted the early 4th century BC texts of Ctesias of Cnidus for his description of the Hanging Gardens:
"There was also, beside the acropolis, the Hanging Garden, as it is called, which was built, not by Semiramis, but by a later Syrian King to please one of his concubines; for she, they say, being a Persian by race and longing for the meadows of her mountains, asked the King to imitate, through the artifice of a planted garden, the distinctive landscape of Persia. The park extended four plethra on each side, and since the approach to the garden sloped like a hillside and the several parts of the structure rose from one another tier on tier, the appearance of the whole resembled that of a theatre. When the ascending terraces had been built, there had been constructed beneath them galleries which carried the entire weight of the planted garden and rose little by little one above the other along the approach; and the uppermost gallery, which was fifty cubits high, bore the highest surface of the park, which was made level with the circuit wall of the battlements of the City. Furthermore, the walls, which had been constructed at great expense, were twenty-two feet thick, while the passage-way between each two walls was ten feet wide. The roof above these beams had first a layer of reeds laid in great quantities of bitumen, over this two courses of baked brick bonded by cement, and as a third layer of covering of lead, to the end that the moisture from the soil might not penetrate beneath. On all this again earth had been piled to a depth sufficient for the roots of the largest trees; and the ground, when levelled off, was thickly planted with trees of every kind that, by their great size or other charm, could give pleasure to the beholder. And since the galleries, each projecting beyond another, all received the light, they contained many Royal lodgings of every description; and there was one gallery which contained openings leading from the topmost surface and machines for supplying the gardens with water, the machines raising the water in great abundance from the river, although no one outside could see it being done. Now this park, as I have said, was a later construction."
Quintus Curtius Rufus (active 1st century AD) referred to the writings of Cleitarchus, a 4th century BC historian of Alexander the Great, when writing his own History of Alexander the Great:
"The Babylonians also have a citadel twenty stades in circumference. The foundations of its turrets are sunk thirty feet into the ground and the fortifications rise eighty feet above it at the highest point. On its summit are the hanging gardens, a wonder celebrated by the fables of the Greeks. They are as high as the top of the walls and owe their charm to the shade of many tall trees. The columns supporting the whole edifice are built of rock, and on top of them is a flat surface of squared stones strong enough to bear the deep layer of earth placed upon it and the water used for irrigating it. So stout are the trees the structure supports that their trunks are eight cubits thick and their height as much as fifty feet; they bear fruit as abundantly as if they were growing in their natural environment and although time with its gradual decaying processes is as destructive to nature's works as to man's, even so this edifice survives undamaged, despite being subjected to the pressure of so many tree-roots and the strain of bearing the weight of such a huge forest. It has a substructure of walls twenty feet thick at eleven foot intervals, so that from a distance one has the impression of woods overhanging their native mountains. Tradition has it that it is the work of a Syrian King who ruled from Babylon. He built it out of love for his wife who missed the woods and forests in this flat country and persuaded her husband to imitate nature's beauty with a structure of this kind."
Strabo (c. 64 BC – 21 AD) described of the Hanging Gardens as follows, in a passage that was thought to be based on the lost account of Onesicritus from the 4th century BC:
"Babylon, too, lies in a plain; and the circuit of its wall is three hundred and eighty-five stadia. The thickness of its wall is thirty-two feet; the height thereof between the towers is fifty cubits; that of the towers is sixty cubits; and the passage on top of the wall is such that four-horse chariots can easily pass one another; and it is on this account that this and the hanging garden are called one of the Seven Wonders of the World. The garden is quadrangular in shape, and each side is four plethra in length. It consists of arched vaults, which are situated, one after another, on checkered, cube-like foundations. The checkered foundations, which are hollowed out, are covered so deep with earth that they admit of the largest of trees, having been constructed of baked brick and asphalt – the foundations themselves and the vaults and the arches. The ascent to the uppermost terrace-roofs is made by a stairway; and alongside these stairs there were screws, through which the water was continually conducted up into the garden from the Euphrates by those appointed for this purpose, for the river, a stadium in width, flows through the middle of the City; and the garden is on the bank of the river."
Philo of Byzantium (writing around 250 BC), whose list of the Seven Wonders of the Ancient World we use today, was credited with the following description:
"The Hanging Gardens [is so-called because it] has plants cultivated at a height above ground level, and the roots of the trees are embedded in an upper terrace rather than in the earth. This is the technique of its construction. The whole mass is supported on stone columns, so that the entire underlying space is occupied by carved column bases. The columns carry beams set at very narrow intervals. The beams are palm trunks, for this type of wood – unlike all others – does not rot and, when it is damp and subjected to heavy pressure, it curves upwards. Moreover it does itself give nourishment to the root branches and fibres, since it admits extraneous matter into its folds and crevices. This structure supports an extensive and deep mass of earth, in which are planted broad-leaved trees of the sort that are commonly found in gardens, a wide variety of flowers of all species and, in brief, everything that is most agreeable to the eye and conducive to the enjoyment of pleasure. The whole area is ploughed in just the same way as solid ground, and is just as suitable as other soil for grafting and propagation. Thus it happens that a ploughed field lies above the heads of those who walk between the columns below. Yet while the upper surface of the earth is trampled underfoot, the lower and denser soil closest to the supporting framework remains undisturbed and virgin. Streams of water emerging from elevated sources flow partly in a straight line down sloping channels, and are partly forced upwards through bends and spirals to gush out higher up, being impelled through the twists of these devices by mechanical forces. So, brought together in frequent and plentiful outlets at a high level, these waters irrigate the whole garden, saturating the deep roots of the plants and keeping the whole area of cultivation continually moist. Hence the grass is permanently green, and the leaves of trees grow firmly attached to supple branches, and increasing in size and succulence with the constant humidity. For the root [system] is kept saturated and sucks up the all-pervading supply of water, wandering in interlaced channels beneath the ground, and securely maintaining the well-established and excellent quality of trees. This is a work of art of Royal luxury [lit. 'riotous living'], and its most striking feature is that the labor of cultivation is suspended above the heads of the spectators."
There is some controversy as to whether the Hanging Gardens were an actual construction or a poetic creation, owing to the lack of documentation in contemporaneous Babylonian sources. There is also no mention of Nebuchadnezzar's wife Amyitis (or any other wives), although a political marriage to a Median or Persian would not have been unusual. Herodutus writing about Babylon closest in time to Nebuchadnezzar II, does not mention the Hanging Gardens in his Histories. However, it is possible that cuneiform texts on the Hanging Gardens may yet be found.
To date, no archaeological evidence has been found at Babylon for the Hanging Gardens. It is possible that evidence exists beneath the Euphrates, which cannot be excavated safely at present. The river flowed east of its current position during the time of Nebuchadnezzar II, and little is known about the western portion of Babylon.
A recent theory proposes that the Hanging Gardens of Babylon were actually constructed by the Assyrian King Sennacherib (reigned 705 – 681 BC) for his palace at Nineveh. Historian Stephanie Dalley posits that during the intervening centuries the two sites became confused, and the extensive gardens at Sennacherib's palace were attributed to Nebuchadnezzar II's Babylon.