bastion means strength, tall building, surrounded by walls. It is a term of origin in the French language. Stronghold also means something that serves as a defense, that sustains something.
Baluarte is a fortification structure of military architecture, it is a work made to defend people, as it has a heavier and stronger structure, bastions are usually on corners, in a pentagon shape, and supported by walls of masonry.
The first bastion work appeared in Italy, in the 15th century, but became better known in the second half of the 17th century, with the Marquis de Vauban, in France. Initially, the bulwark was used by artillery, to cross fire with the other bulwarks, and to deter enemy attack.
There are several types of bastions, double, flat, truncated, simple, half-bulwark, regular, real, terraplanado, etc.
In the figurative sense, bastion means safe place, support and is used to describe the essential elements that serve as a foundation and that sustain someone or something. Ex: Music is one of the strongholds of culture.