Old stuff is cool, especially if you're a hipster who was into it before it was cool. Like Hipster Kitty. In this book, we get glimpses of two old cities that are both different from each other and both important to Alanna's development as a character.
First, Sir Myles brings Alanna to the ruins of a settlement inhabited by the Old Ones, a (you guessed it) really old civilization. Here's how it looks: "The remains of stone walls stretched before them in neat rows, forming buildings and rooms inside the buildings" (6.145).
Since Myles is a scholar, he's IDed some of the buildings (the main house, the armory, etc.). But it's Alanna who makes the most important discovery: how to open the armory door. Inside that passageway, she finds a magical sword that saves her life more than once. So this visit to an ancient city is clearly a win for Alanna.
The Black City, by contrast, is not a good place for Alanna, or any mortal, really. Unlike the ruins of the Old Ones, it hasn't aged one bit: "There was no sand in the Black City, no dust—nothing to show that centuries had passed since people lived there. The alien buildings—beautifully and carefully carved—rose without break from the rocks of the streets." (7.78)
And while Alanna found a helpful magical item in the Old Ones' city, she finds magical enemies in the Black City: the Nameless Ones or Ysandir, who like to eat children's souls. (Intrigued? Check out their "Character Analysis for more on these delightful immortals.) Since Alanna has been training and becoming more awesome over the course of the book, she can team up with Jonathan to take them down—with the help of her magic sword helps, too. Interesting to note that the artifact from one ancient city helps destroy evil beings in another ancient city, hm?
The Same but Different
So, there's an obvious thematic contrast between the two cities, but let's dig down a little deeper. When Sir Myles and Alanna are exploring the ruins at Olau, Alanna is asking questions like what is this stuff made of? He answers: "It looks like bronze or copper, but it polishes to a higher shine than new metal. I think it's the coating they were dipped in. The Old Ones treated everything with it—metal, wood, paper. Anything that might show age. They were terrified of aging" (6.148).
So…let's get this straight. One city, now in ruins, was populated by the mysterious Old Ones who were afraid of aging. The other city, totally still intact, is populated by the also-mysterious Nameless Ones, who keep themselves going by killing and consuming innocent children. The fact that a sword that came from a dead civilization is able to defeat a deathless terror suggests to us that there is far more power to be had in nature and the natural life cycle. The Nameless Ones removed themselves from nature by attempting to become immortal and preserve their city forever—but eventually, kids come along and destroy them. One generation gives way to the next.