Rock-Filled Wire Cage Used in Castle Fortification
Puzzle 5 of Women Inventors Hard Pack
Question is: Rock-Filled Wire Cage Used in Castle Fortification
and the answer is: GABION
Word Meaning:
GABION — (historical, military) A cylindrical basket or cage of wicker which was filled with earth or stones and used in fortifications and other engineering work (a precursor to the sandbag).
Definitions from Wiktionary.