Chéng xū literally combines chéng (city wall, fortress) and xū (ruins, abandoned settlement), referring specifically to the crumbling remains of an ancient city wall or fortified structure — not just any ruins, but those with defensive architectural significance. It evokes historical layers, often found in archaeological or literary contexts describing sites from dynastic periods like the Warring States or Han.

This term carries a poetic, slightly melancholic tone and appears more frequently in formal writing, historical narratives, or travel descriptions than in everyday speech. Unlike generic words for 'ruins' (e.g., fèixū), chéng xū emphasizes the original function as a military or administrative boundary. It is commonly associated with earthen ramparts, broken watchtowers, or weathered stone foundations visible at heritage sites across northern China.