What is "teichoscopy"

Teichoscopy or teichoscopia, meaning "viewing from the walls," is a recurring narrative strategy in ancient Greek literature. One famous instance of teichoscopy occurs in Homer's Iliad, Book 3, lines 121-244.

The passage begins with Helen approached in her chamber by Iris, disguised as her sister-in-law Laodice, the daughter of Priam. Helen is then led to the walls of the Skaian gates, where she is summoned by Priam, who asks her to point out the Achaean heroes she sees on the Trojan plain. Below her, the two armies are preparing for the duel between Menelaus and Paris. Helen identifies Agamemnon, Odysseus, Telamonian (Greater) Ajax, and Idomeneus. She also mentions that she does not see her brothers Castor and Pollux, who unbeknownst to her are already dead back in Greece. After this scene, the duel commences, with both armies praying to Zeus and the rest of the gods on Olympus to open the action.