You are a construct.
You were brought into existence to protect the fortress. That is the first thing you know.
The polished steel armor that makes you up is strong. It will allow you to adequately fulfill your directive. It does so today. The enemy soldiers break through the stone walls. A strong knight, wielding a morningstar, enters first. He swings his weapon at you. You fight back. You are killed, but your body blocks the entrance long enough for your fellows to arrive.
You were brought into existence to protect the fortress. That is the first thing you know.
The dented steel armor that makes you up is weak, but it will still function. You are ordered to remove the corpses of the enemies and burn them. You are unsure how this protects the fortress, but you do it anyway. When you do, you find, in the hands of one of them, a vial of some sort of potion. It is green and bubbling. You attempt to safely dispose of it.
You were brought into existence to protect the fortress. That is the first thing you know.
The shrapnel that makes you up is barely held together with a piece of string. You are unsure whether or not the string is you. Today, the enemy has returned to the fortress. They launch more potions at the walls, which disintegrate. You try to catch one in midair, but you feel part of you fading away. You have to protect the fortress. But how?
You see the catapults in the distance. They are preparing to fire again. By stopping them, you will fulfill your directive. But they are too far away. How can you stop them? You figure it out.
The piece of shrapnel that makes you up flies across the battlefield. It hits, with near-miraculous precision, slicing through the rope that would have allowed a catapult to fire. You throw again, and again, until you are only a string. But there is still one more catapult.
The small piece of string that makes you up snakes across the battlefield, under the lines of now-fearful soldiers. You sneak up the arm of the catapult, tying yourself around it. It fires, and you pull with all your might. The potion slams into the ground, halfway between the catapult and the fortress, as both the weapon and you break.
You were brought into existence to protect yourself. That is the first thing you know.
The stone walls that make you up are damaged but being repaired. The constructs that protect you work to rebuild you. The enemies have only returned once since you awakened. You allowed them to enter, then shifted your hallways to trap them in an endless maze. They soon surrendered. They have not returned since. You are protected.
You are a fortress.