The circle of blood is often simply called the Blade's Edge Arena.
It is located in Blade Edge Mountain and can be entered in the game world, causing the player to be flagged for Free For All pvp, allowing even same facton players to kill each other while within it.
It is also one of the 5 current possible location for Arena battle.
The circle of blood is better known for its massive bridge, which allow players to break line of sigh with each other as well as gain protection from certain effect or pet by playing with the elevation difference. Most strategic element about this arena involve using the pillars of the bridge in some fashion, or trying to seperate the enemy team between the higher bridge and the ground level.
Like all Arenas, after 5 minutes, 2 Shadow Sight power ups will appear on the pillars that are on each side of the bridge. When a player touch the power up, he gets a debuff that greatly increase his stealth detection but also increase all damage taken by 5% for several seconds.