bastion in English:

The royal navy of England hath ever been its greatest defense and ornament; it is its ancient and natural strength; the floating bulwark of our island.

This place is a catholic stronghold.

The thief has to be in here. I'm sure somewhere around is his stronghold so if we can just find that we've got him.

Although Iran is nowadays known for being a stronghold of Shia Islam, most Persian Muslims were Sunni until the XVth century.