In order to access the chest, you are going to have to obtain the four ornamental keys from the Phylakes. You must assassinate the four key-carrying Phylakes, who will drop an ornamental key as part of their loot.
How to Assassinate the Phylakes
Phylakes will make themselves available after you complete the Gennadios the Phylakitai quest. However, you will not be able to kill the Phylakes until you are a higher level than the Phylake you are fighting.
They are going to be a tough fight, and they also like to make things harder by calling in reinforcements. If you want the most optimal fight, you will need to lure the Phylakes away from guards to minimize the amount of enemies you have to fight.
Another trick to Phylakes is that they travel by mount, which can make them harder to fight. To make the fight easier on you, you are going to want to get them off their mount. Another helpful tip is to try and assassinate them by sneaking behind them and doing the deed quickly.
The Phylakes will drop legendary gear and a quest item if they are a key carrier, and on top of that, you will obtain XP.
Getting the Eye of Horus Chest
After you defeat the first Phylake, you will receive a contract, which, in combination with the four ornamental keys you receive from the Phylakes, will take you to a fishing village in Herakleion Nome.
You will need to find Abar in the north side of the village, who will agree to give you a key if you defeat the crocodiles on the east side.The crocodiles are not an easy fight, and the best strategy is to eliminate them one by one and quickly.
After you defeat the crocodiles, go back to Abar to receive the final key and a quest location. The quest location will take you to the treasure location. You will have to dive underwater to access the chest containing the Black Hood Legendary Outfit.
We hope this guide helps you get to the Eye of Horus chest. Let us know in the comments how you are taking down the Phylakes.