Fortress guards are level 52 soldiers. They are around and inside the Black Knight's Fortress; however, their exact status within the Kinshra hierarchy is unclear. Their weapons include swords, spears, and halberds. Although spears and halberds are generally two-handed weapons, these guards can use halberds in conjunction with bronze sq shields.
When you talk to a fortress guard he might say "Of course the officers have some nice, elite black plate armour, but thats nothing we grunts can ever dream of." indicating they are a low position in the Kinshra army, possibly foot soldiers.
They appear to have red crossed details on the top of their Bronze helm when the med helm obtained by players will not.
When spoken to after completing Black Knight's Fortress, they will tell you "Get lost. This is private property" but after responding with "But I work here", they will say "Well, this is the guards' entrance. I may be new here, but I can tell you're not a guard." (Note that not ALL guards are new due to the fact that every guard outside the fortress says that.)
If you are wearing Full Black armour (Or Elite Black), the Fortress Guards will instead say "Sorry, sir, but I'm under strict orders not to chat while on duty.".
After the Evolution of Combat update, Fotress Guards now have a higher level than the Black Knights, their superior officers.