When the B is capitalized in ‘Bastille’, it refers to a fortress in Paris, built in the 14th century: a prison until its destruction in 1789, at the beginning of the French Revolution.
Bastion, on the other hand, means a fortified area or stronghold, frequently implying a rampart or irregular fortification surrounding the base of a structure: “Fortress build in the 18th century India were bastions o safety.”
It also means ‘an institution serving as an example of strength’: “Warren Buffet is considered a bastion of respectability in the world of shares and trading.”