In the story from chapter 11 from the Book of Genesis of the Bible, there had been a united humanity of the generations after the Great Flood who spoke a single language. Migrating from the east, they settled in the land of Shinar, where they started to build a city with a large tower that would have its top in the heavens, so that they wouldn't be scattered abroad upon the face of the earth. We can assume that, for this reason, it would have served as a large marker that still would be seen at very large distances. In Genesis 11:6-8, the LORD saw what they were up to and said:
"If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them. Come, let us go down and confuse their language so they will not understand each other. So the LORD scattered them from there over all the earth, and they stopped building the city."
There is a Sumerian myth that is similar to that of the story of the Tower of Babel, called Enmerkar and the Lord of Aratta. This myth talks about the building of a massive ziggurat in Eridu by Enmerkar; the king of Uruk. (According to Sumerian mythology, Enmerkar was the mortal son of the god Utu and Aia.) Here he demanded a tribute of precious materials from Aratta for its construction, at one point reciting an incantation imploring the god Enki to "disrupt" (according to Samuel Noah Kramer's translation) the linguistic unity of the inhabited regions - named as Shubur, Hamazi, Sumer, Uri-ki (Akkad), and the Martu land.
The part of the Sumerian epic entitled "Enmerkar and the Lord of Aratta" (here translated by Samuel Noah Kramer) seems to be related to the story of the Tower of Babel and the confusion of tongues:
"Once upon a time there was no snake, there was no scorpion,
There was no hyena, there was no lion,
There was no wild dog, no wolf,
There was no fear, no terror,
Man had no rival.
In those days, the lands of Subur (and) Hamazi,
Harmony-tongued Sumer, the great land of the decrees of princeship,
Uri, the land having all that is appropriate,
The land Martu, resting in security,
The whole universe, the people in unison
To Enlil in one tongue [spoke].
(Then) Enki, the lord of abundance (whose) commands are trustworthy,
The lord of wisdom, who understands the land,
The leader of the gods,
Endowed with wisdom, the lord of Eridu
Changed the speech in their mouths, [brought] contention into it,
Into the speech of man that (until then) had been one."
Today in the place of Al-Mahawil in Bābil (Babel), Iraq, we can find the remains of a ziggurat dedicated to Marduk in the city of Babylon of the 6th century BC, known as the "Etemenanki"; which translates to: "temple of the foundation of heaven and earth". In 1913, archaeologist and architect Robert Koldewey started its excavation after it had been rediscovered by the native Arabian population. It had been regarded to be the ruins of the Tower of Babel.
The structure was also known as the "Tower of Jupiter Belus" (Belus translates like Bêl to "Lord") and had been Hellenised by Herodotus to "the Tower of Zeus Belus". A cuneiform tablet from Uruk, written in 229 BC, states that the tower was made up of seven terraces. After the fall of Babylon it never had been restored. Its ruins can be found with Google Maps at coordinates: 32 32'10N, 44 25'14E.
Ruins of the Etemenanki.
(Click for a larger image)