Steadfast

+3 to maximum Fortification
Regenerate 0.1% of Life per second per Fortification [1]

Steadfast is a notable passive skill that increases the maximum stacks of fortify.

Anointment

Blight anointment to unlock the passive:

Oil #1	Oil #2	Oil #3	Outcome
Sepia Oil	Golden Oil	Golden Oil	Steadfast	+3 to maximum Fortification Regenerate 0.1% of Life per second per Fortification

Version	Changes
3.21.0	The Steadfast Notable Passive Skill now provides +3 to maximum Fortification (previously +4), and also now has "Regenerate 0.1% of Life per second per Fortification". The entry small Passive Skill in the Steadfast cluster no longer provides "Fortifying Hits grant 30% increased Fortification", and instead provides "+1 to maximum Fortification".
3.19.0	The entry small Passive Skill in the Steadfast cluster that provides increased Fortification for Fortifying Hits now has a value of 30% (previously 20%). The top of the Steadfast cluster now consists of two small Passive Skills that each provide 40% increased Fortification Duration (previously one small Passive Skill that provided 20% increased Fortification for Fortifying Hits).
3.16.0	Change the Fortify mechanic so it is given as stacks of Fortification, which is gained based on how much melee damage you deal. No longer grants 10% increased Effect of Fortify on you, 10% increased Effect of Fortify on you while Stationary or 30% increased Armour while you have Fortify. Instead, it now grants +4 to maximum Fortification. [Undocumented This change was not documented by any official sources. It was discovered through player testing or datamining.]
3.7.0	Introduced to the game