Tevinter
The ruling powers of Tevinter made a calculated decision to raise a magical barrier, an authorized move executed by the state itself. Driven by a desire to consolidate power, control dissent, and safeguard Tevinter from both internal conflicts and external threats, the Archon emerges as the face of this grand endeavor. Publicly claiming credit for the barrier's construction, the Archon paints a vision of safety, stability, and prosperity for Tevinter.

Amidst the intricate dance of shifting alliances and political intricacies, the Archon, a master tactician, recognized the necessity of a unifying force. Proposing the construction of the magical barrier, the Archon aimed to solidify authority, instill a sense of security, and quell unrest within Tevinter's borders. The barrier became a symbol of the Archon's leadership, a shield against the chaos that lurked beyond the nation's boundaries.

Behind the scenes, the Black Divine played a crucial role in the magical intricacies of the barrier. Rather than seeking public acclaim, the Black Divine embraced a clandestine role, skillfully maintaining the barrier's integrity from the shadows. This enigmatic figure remained hidden, dedicating themselves to the safety of Tevinter with a sense of silent duty.

The unexpected discovery of a large red lyrium vein within the magical construct ultimately leads to the barriers' fall and the Black Divine's death. This malevolent force, drawn to the magical energies that sustain the barrier, begins to corrupt and corrode the Black Divine from within. Unbeknownst to the Archon and the citizens who revere the barrier, an internal struggle unfolds, placing the entire magical construct at risk.

As the Black Divine's life force wanes, a sudden and catastrophic failure grips the barrier. With the one who silently maintained it meeting an untimely demise, the magical shield crumbles, exposing Tevinter to the outside world once more. The tragedy unfolds in the present, leaving the citizens in shock and the once-revered barrier now a memory of both protection and unforeseen loss.

TLDR;;

• WHAT THE PEOPLE OF TEVINTER KNOW (PUBLIC): Tevinter put up a barrier to protect itself from the outside world's influence.
  
• WHAT THE HIGHER-UPS KNOW (SECRET): The barrier was put into place because Tevinter worried about the repercussions of Fen'Harel removing the Veil. It was also put into place to keep others out of Tevinter, and protect their carefully crafted magistrium from outsider influence with a rising level of slave rebellions in 9:45.
  
• WHO DID IT? The barrier was created by the Black Divine, but the credit was claimed by the Archon.
  
• WHAT BROUGHT IT DOWN? The Black Divine's death (as he sustained the magic for the barrier) due to spreading red lyrium.