Defeat the Deathless Warriors
You’re by the entrance to another huge gate. There are several Archers at the back of the area, near the gate. Guards are coming in there too, but they move forward more aggressively to seek you out.
Use light weaponry to detonate the Greek Fire urns as the early rushers get to you. That thins their numbers. You’re able to run between the pillars where you begin and pick off smaller clusters of Deathless.
Beware Guards that are willing to climb and attack you from above. If you see one of them getting onto the pillars, either attack him aggressively before he can jump on you, or run away so that he doesn’t have a target!
Poison Arrows continue to be your best weapons against the heavier Deathless, but don’t waste those precious shots on Archers or single targets. Use regular ranged weaponry for the former, and melee executions for the latter.
Win this battle and watch a small scene. Enter the Citadel afterward and look for the Citadel Gate Base Camp.