The Ouranios Alliance responded to the loss of the outpost with overwhelming force. They built up a vast force, recruiting men from each of the four sects and marching upon the recently captured fort, that Nyx, in a symbolic rebirth, had chosen to be called Aethelgard. The siege of Aethelgard was about to begin.
Nyx realised that they could not stand their ground against such a sizeable army indefinitely. Their chance lay, in fact, in inflicting such a large scale of losses that the retreat would be an option and then to use guerrilla warfare methods to finally attack the Ouranios army as a battering ram against their hopes of victory, in order to gradually weaken them. He adopted a layered approach to defense, using both the topography and the structure of the fortress itself to his advantage.
Their initial line of defense was a network of concealed traps designed for ambush in the surrounding wood. Using his mastery of shadows, Nyx concealed his soldiers within the trees, allowing them to pick off advancing Ouranios scouts and disrupt their supply lines. He also used illusions to build illusions of armies drawing enemy attention and causing chaos, as a ploy.
When the Bulwark army reached Aethelgard the main Ouranios army bore the brunt of a hail of arrows and projectiles from the fortress walls. The engineers are obligated to fortify the walls and to build a new line of bulwarks, including ballistae and catapults, provided by Nyx. He also sent his shadow mages to plant a heavy veil of fog around the fortress, introducing more concealment of their defenses, and obscuring enemy attempts at direct attacks.
The Ouranios garrison conducted a number of assaults on the fortress walls, however, with massive casualties on each occasion. Nyx used a "defense in depth" approach, meaning that, if the enemy managed to penetrate the outer defences, they would then have to contend with another tier of defences within the fort. He had already built up a system of linked bunkers and strongpoints whereby his troops could retreat and consolidate, simultaneously harassing the enemy from a variety of directions.
During one particularly fierce assault, the Voreios sect, known for their brute strength and heavy armor, managed to breach a section of the outer wall. They poured into the fortress, confident of victory. But Nyx had anticipated this. He commanded his shadow weavers to create an illusion sequence in the garrison which would produce the effect of phantom hallways and false pathways. The Voreios soldiers became disoriented and separated, easy targets for the Daimonas defenders who knew the layout of the fortress intimately.
While, Nyx and a few of his most trusted warriors, conducted the shelking operation. They (sappers) attacked from behind the Voreios antagonists on the underground tunnels leading to the fortress, cut off their escape and trapped them against its outer wall. The Voreios soldiers, caught between two forces, were quickly overwhelmed and forced to surrender.
Following a number of days of fighting, the Ouranios siege had become exhausted. They had taken devastating losses, had morale down, and had achieved very little in their attempt to capture the fortress. Nyx understood that it was finally the stage of his plan to be carried out.
Under the cover of another magically created fog, Nyx led a large portion of his army out of the fortress through a secret tunnel. They moved fast and unnoticed, encircling the Ouranios army and attacking their rear supply lines. This obligation caused the commanders of Ouranios to shift a substantial number of their troops in order to safeguard their provisions, thus bringing their siege to a disadvantage.
Recognising their opportunity then, the "Andromeda's Guard-resspite' (Daimonas) and the troops of the Swamp Commander in Aethelgard launched a surprise raid, which smashed the siege and drove the rest of the Ouranios legion grunts into retreat. The siege of Aethelgard was a decisive win for Nyx and his army, the embodiment of his strategic prowess as also of the rising strength of the Daimonas rebellion.