What Is Rumbling in Attack on Titan? How Is It Activated?

For centuries, the island of Paradis was protected by walls made of hardened Colossal Titans. In a world that was making constant technological advancements, these Titans were Eldia's last card against those who would wish to see it destroyed. 

When the Eldian people were moved to Paradis, King Karl Fritz declared that

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This event would come to be known as The Rumbling. 

The threat was effective since the idea of millions of Colossal Titans marching on the human population was terrifying. But unknown to most, Karl Fritz had no intentions of causing such a catalytic event. In a vow with the Founding Titan, the King had renounced war, ensuring that his successors would be able to cause no harm to the world.

However, towards the end of the Attack On Titan Manga, Eren Yaeger succeeded in bringing this doomsday event to life, killing over eighty percent of the planet's human population.

What Are The Three Walls?

The outermost wall is called Maria, and it's the first barrier between Paradis and the rest of the world. The second wall within Maria is called Rose, and it separates the upper-class families from the poor ones. The third and final wall, Sina, separates the royals from the upper class.

These walls are 50 meters tall, and for the most part indestructible. Therefore, they act as a barrier against Paradis and the Pure Titans trying to cause trouble.

These walls also had their own church and were religiously worshipped by the 'Wallists' as the protectors of humanity.

Until the beginning of the AoT series, the humans inside the walls had no idea that there were Titans within it. At the will of the Founding Titan, millions of Colossal Titans had hardened themselves to form a barrier against the outer world. And only at the command of the Founding Titan was it possible to free these Titans and use them to cause The Rumbling.

What Is The Purpose Of The Rumbling?

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The Rumbling was an empty threat by King Karl Fritz to protect Paradis for as long as he could.

Though he said that the Eldians could use the Wall Titans to flatten the planet, King Fritz had sworn an oath that prevented his successors from using these Titans.

Karl acknowledged that an oath like that would leave Paradis defenseless in the future. Still, he believed that given the Eldian Monarchy's crimes in the past, such a future was inevitable and deserved. Therefore, his only goal was to protect his people for as long as possible, and after that, they would pay penance for their ancestors' wrongs.

What Were The Conditions To Activate The Rumbling?

There were two conditions to fulfill in order to trigger The Rumbling. 

First, only the Founding Titan could command the Wall Titans and unleash them onto the planet. Second, for the spirit of Ymir to carry out the will of the Founding Titan, the carrier of the Titan had to be of royal blood.

The second condition directly contradicted Karl's oath, though.

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Since Karl Fritz renounced violence, no descendant of his could command the Wall Titans to commit destruction. This is why The Rumbling was considered an "empty threat."

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However, things took a drastic change when Eren came into possession of the Founding Titan.

And it's why Eren and Zeke's unlikely alliance was so significant to the plot.

Since Eren wasn't royal, he wasn't bound by Karl Fritz's oath of non-violence. But he couldn't use the full power of the Founding Titan to command the Wall Titans.

On the other hand, Zeke's royal DNA would make it possible for him to command Ymir into unleashing the Titans. But the oath prevented him from doing so.

Together, however, the two could bypass these conditions and trigger The Rumbling.

Eren would later figure out that Zeke's true goal was to sterilize the Subjects of Ymir and that against a royal's command, his own wasn't good enough. With no other option, Eren then convinced the spirit of Ymir to free herself from her oath to serve the royals and thus triggered the Rumbling.

What Happened After Rumbling?

Seeing Mikasa sever Eren's head, Ymir decided to let go of her control over the Founding Titan, effectively putting an end to the Rumbling and the powers of all Titans. Ymir saw herself reflected in Mikasa's love for Eren and was set free Mikasa's choice — a choice she could never make herself. 

Three years after the Rumbling, the world was in relative peace. The Marleyen government sent ambassadors to Paradis to start peace negotiations. On their way, they were informed that the remaining Yaegerists had formed an army to defend Paradis from the outside world.