(formal) a group of people or a system that protects a way of life or a belief when it seems that it may disappear (Oxford)
a place that military forces are defending (Oxford)
something that keeps or defends a belief or a way of life that is disappearing or threatened (Cambridge)
Singapore was the last bastion of British defences in South-East Asia. (Oxford)
British public schools are regarded as one of the last bastions of upper-class privilege. (Cambridge)
last bastion of British defences
Fortress
Stronghold
Weak spot
Bastion