- "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."
One of the earliest Wonders in the game, the Hanging Gardens are not generally worth the time and effort. The major selling point of this Wonder is 15% bonus growth to all cities. This may sound tempting, until you realize that 15% applies to the excess Food the cities have (the amount of Food left over after subtracting the Food consumed by Population), not the total Food. If you open the Toggle City Details on the city panel, except for a few civilizations or city locations, rarely ever you will have an excess of 10 Food, which in that case will result in 1.5 Food extra, less than a Grassland tile with no improvement. Even if you have a lot of excess Food in your cities, its worth is a bit wasted if your cities have Housing problems, which are quite common in practice. The +2 Housing bonus is helpful to the city that builds the Hanging Gardens, but since they do not provide any other bonus yields, you may want to forgo building them unless you have multiple cities that can support the additional Population. The civilizations that can make optimal use of this Wonder are the ones with bonuses to generate extra Food and infrastructure that provide Housing early in the game, most notably the Indians (Stepwell), the Kongolese (Mbanza), the Maya (Farms), and the Khmer (Aqueducts and Holy Sites). Civilizations that love settling next to Floodplains can also try to build this Wonder, most notably Egypt (tier 2 Floodplains bias), since Floods can provide a healthy amount of excess Food to grow your cities, but again, you would have to invest a lot into Housing infrastructure to truly make this Wonder worthwhile.
When playing in the Heroes & Legends game mode, this Wonder is slightly more worth building, as it prolongs the Lifespan of all Heroes that you earn. It is especially useful for Heroes that are used for conquest and militaristic purposes, but not so much for Heroes who rely on their powerful Charge-based abilities more than their prowess on the battlefield. It is also worth noting that 10% longer Lifespan means 5 more turns for Sun Wukong, 4 more turns for Himiko, and only 3 more turns for anyone else, so it may not be worth investing in a Wonder that is largely useless otherwise unless you know you can pull off miracles on those extra turns. This extra Lifespan seems even more pointless when you consider that summoning or recalling a Hero in a city with a Shrine grants the same bonus.
The Hanging Gardens may not have even existed, much less been a “wonder”; no Babylonian source mentions them, and there is no archaeological evidence for them (unlike for other ancient wonders of the world). The primary evidence for the Gardens comes from several Greek and Roman texts – how they were created, why they were created, their size and variety, even how they were watered. According to these, Nebuchadnezzar II constructed the Gardens c. 600 BC for his (obviously spoiled) homesick Median wife Amytis, who missed the green hills of her birthplace. The “historical” sources also state that the Gardens were an ascending series of terraces (much like a ziggurat) built of mud bricks and containing all manner of plants. The base was supposedly 400 feet square, and the whole mass rose 75 feet into the very dry air; estimates are that the gardens would have required 8200 gallons of water a day to keep the plants alive in Babylon. If the Gardens did exist, it is assumed these were destroyed sometime during the first century AD.