Obelisk of Babylon: in some lists, one of the Seven Wonders of the Ancient World. It did not exist.
In the first century BCE, Diodorus of Sicily, probably quoting Ctesias of Cnidus, tells the following legend about queen Semiramis of Assyria:
She quarried out a stone from the mountains of Armenia, which was forty meters long and seven meters wide and thick; and this she hauled by means of many multitudes of yokes of mules and oxen to the river and there loaded it on a raft, on which she brought it down the stream to Babylon; she then set it up beside the most famous street, an astonishing sight to all who passed by. And this stone is called by some an obelisk from its shape, and they number it among the seven wonders of the world.note[Diodorus, World History 2.11.4-5; tr. C.H.Oldfather.]
This is all we know about this monument. There are no cuneiform references to it, and the whole anecdote sounds like a story from Egypt that has been transferred to Babylonia; the fact that Semiramis is not a historical figure does not contribute to the plausibility of Diodorus' story. Still, it can not be excluded that an Assyrian ruler decided to erect an obelisk like the ones the Assyrians had seen in Egypt.