All 6 Uses

bastion
in
1776, by McCullough
(Edited)

A newly completed bastion at Cobble Hill, below Prospect Hill and fully a half mile nearer to Boston, was described in the Providence Gazette as "the most perfect piece of fortification that the American army has constructed during the present campaign."
p. 67.3

bastion = defensive fortification
The huge bastions that encircled Boston were left standing, but only a holding force under General Ward remained to keep watch.
p. 112.6

bastions = defensive fortifications
When finished, the large square bastion of Fort Stirling, mounting eight cannon, was expected to command the East River and New York just as Dorchester Heights commanded Boston and its harbor.
p. 126.7

bastion = defensive fortification
Each of these bastions was to be surrounded with a broad ditch and all were to be connected by a line of entrenchments reaching a mile or more.
p. 128.1 *

bastions = defensive fortifications
At the first report of the Throg's Neck landing, Washington knew the Harlem Heights bastion had become a trap.
p. 230.3

bastion = defensive fortification
Despite its formidable presence high over the river, its steep, rockbound approaches, Fort Washington was, in several ways, not the impregnable bastion it seemed.
p. 237.1

Definitions:

(1) (bastion)
a strong defender or reliable example of something -- like a fortress or a person upholding a principle
(2) (meaning too rare to warrant focus)