Fortification. a projecting portion of a rampart or fortification that forms an irregular pentagon attached at the base to the main work.
2.
a fortified place.
3.
anything seen as preserving or protecting some quality, condition, etc.: a bastion of solitude; a bastion of democracy.
Origin: 1590–1600; < Middle French < Italianbastione, equivalent to Upper Italianbastí(a) bastion, orig., fortified, built (cognate with Italianbastita, past participle of bastire to build < Germanic; see baste1) + -one augmentative suffix
1560s, from M.Fr. bastillon, dim. of O.Fr. bastille "fortress, tower, fortified, building," from O.Prov. bastir "build," originally "make with bast" (see baste (1)).