Quest from: Sir Henrik;
Sir Henrik will tell you that the Crusader's shield is in Fort Bulwark on the western outskirts of Cyrodiil. When you reach the place, defeat the enemy outside and enter through the main gate. You'll be encountering some trigger-happy Conjurers in here. Remember to chase them instead of fighting their summons.
Reach (A) and use the turnstile there, then go through the open gate (B). Use another switch there to open up a bridge.
You'll see a puzzle on the floor. Go through the left, center, right, and left tile to open up the passage ahead.
When you're on the lower level, in the cell to the right you'll see Sir Thedret. Free him by using the switch and talk to him. Go through the dungeon, heading West, and when you're in a room with a bridge use the two levers to go further. You'll end up in a room with 4 statues in it - use the switches on them to turn them so they all face the center of the room, and a passage will be open.
You'll reach a big room with a stone chest in the middle and 8 statues by the walls. You now have to take certain objects from the chest and place them in the chests near the statues in a way that's shown on the screenshot below. When you do that, a secret passage will open and you'll be able to grab the shield at last.