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
3.16.0	Change the Fortify mechanic so it is given as stacks of Fortification, which is gained based on how much melee damage you deal. (Undocumented) 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.
3.7.0	Introduced to the game