The Cracking

It all happened at once--a shift, like a god stumbling over a discarded marble--and the world cracked. Sparking lines laced with energy that were once invisible became real as the land tore and collided, forming mountains and caverns and ultimately, a series of sparking, angry portals.
That's when the monsters entered the land.
The area we're focused on was extra unlucky. Before the age of monsters was the age of magic and prosperity. A great city built over centuries soaked in the magic of crossing ley lines that couldn't be found anywhere else in the world. Wizards traveled months to feel the energy seeping from the lines here.
So when the world cracked, so too did the city. And beneath it, 8(probably) portals spun to life. At first, the city's inhabitants remained in their homes. They were shaken from the changes to their world, a smoking mountain slicing through the center of their town, caverns swallowing another section, the air brittle and volitile. They were mourning, so many gone in one single moment.
When the monsters arrived, no one looked up. Those that did ran and continued running for years, desperate to get back, and completely unable to.
Those nomadic years were lonely and desperate, time spent surviving.
When they discovered adventurers seeking glory for killing monsters, the town begged the adventurers to help, and help they did.
A Champion stood out from the travelers, clearly devoted to helping those in need. She was the ultimate push to get the people back into the city even if it was just for a moment. She breach the barrier and helped people gain peace of mind.
She was the start of the temple for a god that must have been dedicated to healing in particular.
So yeah. The portals are the ultimate disaster brought on by a world whose geography changed overnight. These portals brought monsters which now plague so much of this world, but specifically hit this city the hardest.

Type

Metaphysical, Arcane