In chapter seven of The Bad Girls, Mario Vargas Llosa uses something called an allusion to describe the city of Lavapiés, a neighborhood in Madrid. An allusion is a reference to something outside of the literature, typically from mythology, the Bible, or another piece of literature. The purpose of an illusion is to add color, sense, and depth to something without having to do a lot explaining.
For example, if a girl says she feels as if she is wearing a scarlet letter, savvy readers know this is a reference to Nathaniel Hawthorne's The Scarlet Letter, and the girl must feel as if everyone is pointing fingers at her, trying to shame her for some sin. If someone says you are acting as if you were Zeus living on Mount Olympus, you should probably be insulted, since Zeus acts like he is the god above all other gods--and that spells excessive arrogance and pride for us mere mortals. If a competition is described as a "David versus Goliath match up," there is a clear underdog going up against an imposing or formidable foe.
The people who do not know the story or character referenced by these allusions simply keep reading with no harm done; those who understand them experience a richer reading of the literature because they know the reference and they "get it."
The narrator in this novel returns to Lavapiés and he finds it a changed place. Fifty years ago it was a traditional neighborhood with little in the way of the unexpected. Now, he says, it is a Babel, and it has changed into this:
The Spaniards from the neighborhood came from every corner of the country, and with their accents and variety of physical types, they helped to give an admixture of races, languages, inflections, customs, attire, and nostalgia the appearance of a microcosm. The human geography of the planet seemed to be represented in its few blocks.
This reference to Babel is a biblical allusion to a story found in Genesis 11. Until this point in history, everyone in the world spoke the same language. They try to build a tower to heaven, in an attempt to reach the heavens. It is an act not of worship but of pride, so God "confounds" them by giving them all different languages.
Therefore is the name of it [the tower] called Babel; because the Lord did there confound the language of all the earth: and from thence did the Lord scatter them abroad upon the face of all the earth. [verse 9]
Thus, the idea of many people from all "languages" gathered in one place is represented by Babel. This is borne out in the rest of the description of Lavapiés.
The narrator continues his description by saying the neighborhood where he grew up now resembles Babylon, comprised of Chinese, Moroccans, Pakistanis, Indians, Romanians, Ecuadorians, and more. That is the point--it is now a neighborhood which is a multicultural melting pot, just like Babylon (another form of Babel), to which he compares it.
He uses this allusion to make the point that his former neighborhood has become a place where people of all cultures and, of course, languages are represented. As I mentioned above, if you know the reference you get the additional richness of sound imagery--imagine thousands of people trying to build something together and suddenly speaking different languages. What a cacophony of sound that would be, and we can apply that to the description if we know to do so. Those who do not know the Babel reference, the meaning of the description is still clear--it's just missing one sensory dimension.