ירמיהו, פרק נ״ב, פסוק כ״א

The Babylonians stripped Jerusalem of its massive architectural pillars, the sheer scale of which was carefully recorded. The height of each individual pillar stood at eighteen cubits, an elevation roughly equivalent to nine meters [מצודת דוד, ביאור שטיינזלץ]. To determine their massive girth, a measuring cord was used [מצודת ציון]. It took a rope twelve cubits long just to wrap completely around a single pillar [רש״י, מצודת דוד, ביאור שטיינזלץ].

Despite their colossal size, these pillars were not cast as solid blocks of metal. Instead, they were hollow inside, resembling giant pipes [רש״י, מצודת ציון, ביאור שטיינזלץ]. This hollow construction mirrors the design of the altar in the Tabernacle [מצודת ציון]. Because of this empty interior, the measurement of four fingers in thickness does not describe a solid metal structure. Rather, it refers specifically to the thickness of the metal walls that formed the outer shell of the pillar [רש״י, מצודת דוד].