What is "defensive gallery"

Gallery \Gal"ler*y\, n.; pl. Galleries. [F. galerie, It. galleria, fr. LL. galeria gallery, perh. orig., a festal hall, banquetting hall; cf. OF. galerie a rejoicing, fr. galer to rejoice. Cf. Gallant, a.]

1. A long and narrow corridor, or place for walking; a connecting passageway, as between one room and another; also, a long hole or passage excavated by a boring or burrowing animal.

2. A room for the exhibition of works of art; as, a picture gallery; hence, also, a large or important collection of paintings, sculptures, etc.

3. A long and narrow platform attached to one or more sides of public hall or the interior of a church, and supported by brackets or columns; -- sometimes intended to be occupied by musicians or spectators, sometimes designed merely to increase the capacity of the hall.

4. (Naut.) A frame, like a balcony, projecting from the stern or quarter of a ship, and hence called stern gallery or quarter gallery, -- seldom found in vessels built since 1850.

5. (Fort.) Any communication which is covered overhead as well as at the sides. When prepared for defense, it is a defensive gallery.

6. (Mining) A working drift or level.

   Whispering gallery. See under Whispering.