The Souls of Heroes represents a Fable Anniversary main quest that is given to you after you consult the Oracle in Snowspire Village. Jack of Blades is beyond the Bronze Gate, but you still have his Soul Mask.
You need to use it to feed the Archons Shrine with the souls of three heroes if you want to open the gate.
The Souls of Heroes is a rather large quest, because it is divided into three sub-quests, one for each soul that you need to absorb.
The next Fable Anniversary walkthrough includes useful information regarding the whole quest.
Money: 8000 + 570
Renown: 100 + 4406
Trophy: Archons Circle
Head to Archons Shrine and speak to Briar Rose to learn how to open the Bronze Gate. She tells you that the only way to activate the mechanism that will open the gate is by collecting the souls of three Heroes.
These Heroes are already dead, but you can kill each Hero that instructs you how to find a proper soul and take their soul instead. Obviously, this is the Evil path to complete the quest.
Briar Rose says that the first soul needs to be the one of an Arena Champion, so she instructs you to find Thunder in Knothole Glade. If you prefer the Evil side you can kill Thunder after the conversation.
Otherwise return to the Arena. On your way there you can help the guards that are attacked by Summoners. Inside the Arena you must defeat several waves of enemies, but this time they are a combination of Minions, Trolls, Balverines, and Summoners.
As usual, the Slow Time spell can help a lot to thin out their numbers. After you defeat all waves you collect the Arena Soul.
Return to Archons Shrine with the soul and feed it to the mechanism. Briar tells you that the next soul belongs to The Heroine. You can kill her on the spot if the Evil path suits you better. For the Good path travel to Oakvale. Scarlet Robe, your mother, waits for you in the Memorial Garden.
However, the area is swarming with Screamers and the Slow Time is a must if you want to defeat them. After you eliminate all the screamers you acquire your Mothers Soul.
Get back to Briar and release the soul from the Mask. She tells you that the last soul is The Oldest Soul, but she has no idea who that might be. Jack of Blades interrupts the conversation telling you that the Shrine wants the Guildmasters soul.
Briar Rose suggests that he may have an alternative and advises you to travel to Heroes Guild to talk to him. The Guildmaster is actually in the Guild Woods, because you can kill him to get his soul if your character is evil. However, someone in the Guild tells you that the soul mentioned in the inscription must be Nostro.
Therefore, travel to the Lychfield Graveyard and go through the Demon Door to the Old Graveyard Path. There are a few enemies in the area, but the choice is yours if you want to fight them or not. Nostro waits for you in the Circle of the Dead. He informs you that he must be defeated in battle if you want to take his soul.
His Undead followers protect him and you cant actually harm him while he is invisible. Kill a few Undead and then focus your attacks on Nostro while he is visible (shooting him with the bow from a distance seems to be the safest way).
You collect Nostros Soul once you defeat him. Return to Archons Shrine for one last time and release the soul to power up the device and open the Bronze Door. The final battle awaits for you on the other side.