Ekphrasis

One particular kind of visual description is also the oldest type of writing about art in the West. Called ekphrasis, it was created by the Greeks. The goal of this literary form is to make the reader envision the thing described as if it were physically present. In many cases, however, the subject never actually existed, making the ekphrastic description a demonstration of both the creative imagination and the skill of the writer. For most readers of famous Greek and Latin texts, it did not matter whether the subject was actual or imagined. The texts were studied to form habits of thinking and writing, not as art historical evidence.

from Writing about Art by Marjorie Munsterberg.