The Tower of Strength in the Fissure of Woe is of great significance to Balthazar and his army of Eternals. In the similarly named quest, you are asked to free the tower from a Shadow Lord and his forces.
The area outside the Tower of Strength is swarming with units of the Shadow Army. There are generally two types of groups, either several Abyssals accompanied by a few Shadow Mesmers (usually the moving patrols) or Shadow Rangers accompanied by Shadow Monks (these are usually the stationary patrols). In addition, there are three Infernal Wurms around the area, each causing massive damage to any foe that comes nearby.