The Byzantine Gold Coin is the sixth treasure that can be found in Uncharted 2: Among Thieves.
The Byzantine Gold Coin is found in Chapter 2 - Breaking and Entering. Once you've emerged from the sewer, don't make a move. Next to you, you should see some wooden crates stacked next to each other so that they form some sort of L-shape. In the corner of the room nearest those crates is another crate. If you stare at it, you'll no doubt spot the glimmer of the treasure hidden there. Simply walk around the L-shaped obstruction and claim your prize before continuing onward.
- In chronological order, this is the first treasure to be found in the game.