The dome

The dome was a protective spell used by the dome dwelling Aurons to recreate their lost homeland.

History
After the Shadow Lord's invasion of Pirra, the people of Pirra used their magic to command the earth to swallow them. The people of Pirra split into three factions, the Plumes, the Aurons, and the Kerons, and settled on three large islands in an underground sea.

However, the majority of the Auron tribe refused to accept the loss of their homeland. Instead of forging a new life underground, they combined their magic to create a massive dome that covered their island. Inside the dome they created an illusion of Pirra for them to inhabit, but it could only exist if everyone inside believed in it. This lead to a divide among the Auron people, with roughly half the tribe being exiled and stripped of their magic.

The Isle of Illusion
Lief, Barda, and Jasmine were brought to the island of Auron by Penn, the Auron's historian, to observe the dome. They were unable to enter it due to the arrival of two Arach, but were later able to by climbing the caverns and descending into the dome from above. Inside they were confronted by the last of the Dome Dwellers, Auris.

Because the companions knew the projections of the dome were false, they destabilized the spell. Auris used the fullest extend of his magic to prevent the dome from collapsing, but the warmth of the dome attracted hoards of Arach, who devoured Auris. His death finally broke the dome and restored both the island of Auron and their lost magic back to the Auron tribe.

Properties
The dome was created to project the illusion of the land of Pirra, and later, Aurons to inhabit it once the dome dwellers began to die off. It also generated warmth and light.

However, the dome could only remain stable so long as everyone inside believed in the illusion. If even one person questioned the legitimacy of what they were seeing, the dome would fade away. The dome was also not a solid object and could be entered from the side or above.