Age of Arcanum

The Age of Arcanum was the second age of Exandria, following the Founding. It includes the Calamity and ended at the Divergence. There are indications that it lasted thousands of years. During this time, mortals tested the limits of arcane power, challenged the gods who had created them, and brought about the escape of the once-defeated Betrayer Gods. This era has also been called "the Age of Wanton Necromancy," as there were no laws against it at the time.

Migration to new lands
From Vasselheim in Issylra, some mortal races had migrated across the seas. During the Age of Arcanum a prominent civilization was known to exist in the verdant lands of Marquet, with a religious sanctuary called the Vault of Shumas in the Aggrad Mountains. The Dranassar lived in the lands that would later be called Xhorhas in Wildemount. Artifacts from the Age of Arcanum can be found along the Menagerie Coast and the Swavain Islands.

Migration across the seas continued in the Age of Arcanum. During this age, some rock gnomes migrated from Issylra to the continent that would later be called Tal'Dorei.

And it was during the Age of Arcanum that a ring of Issylran warlocks is believed to have fallen in with fiends and produced the first tieflings. Persecuted by religious zealots, some tieflings also sailed across the Ozmit Sea.

Early Age of Arcanum
In the early Age of Arcanum, the dwarven Thomara clan dug into the fallen earth titan in the Zenwick Mountains to exploit a precious metal vein cluster and built a vault city there. The society eventually collapsed into madness and cannibalism. This city and Yug'Voril are both described as being "thousands of years" old in 812 PD, but it's possible Yug'Voril was established earlier, during the Founding.

In the first millennium of the Age of Arcanum, an ancient black dragon-turned-dracolich, Guuthal the Ever-Fed, terrorized the world.

Arcane ambition
As civilization flourished and spread under the guidance of Ioun, mortal mages grew ever more powerful, eventually building entire castles in a day and even learning to create life-forms of their own. Minotaurs were created as living weapons and guardians, and mage engineers built intricate gearkeeper constructs to guard their vaults. A handful of crystal-powered flying cities, including Aeor and Zemniaz, traveled across Exandria. And around six or seven centuries before the Divergence, the greatest sages of the Age of Arcanum managed to experiment with reversing the flow of time without being killed.

The spread of corruption
Over the long course of the Age of Arcanum, the Kuul'tevir, noble predecessors of the lizardfolk, debased themselves with violence and greed, leading to the ruin of their civilization. They had had a god-empress, but she was succeeded by a mere ring of warlocks.

Centuries before the Divergence, the increasingly decadent and cruel society of the drow began to primarily worship Lolth, the Spider Queen.

Acek Orattim, priest of Tharizdun, made his base in Gatshadow Mountain, under which Tharizdun had been imprisoned since the Founding. Through Acek, Tharizdun's power twisted and elevated the mountain, riddled it with a maze of tunnels, and corrupted the surrounding region.

Aspirations of godhood
Driven by the quest for immortality, an unnamed mortal woman challenged and defeated the God of Death, and she took his place in the pantheon (but not his entire portfolio) and became the Raven Queen.

The day after the Raven Queen's ascension, three of the Raven Queen's heroes—Clay, Stone, and Dust—were tasked with removing the body of one of the heroes of "the war" from a city. Told by the Raven Queen to follow Melora's instructions, they split the body into parts and took the parts to various locations, and built temples that their families would protect through the ages: the Clay family tended the Blooming Grove, the Dust family tended the Cinderrest Sanctum on Kravaraad, and the Stone family tended the Menagerie.

Though the other gods quickly destroyed the secrets to the Raven Queen's ritual, her achievement would inspire two dark archmages to world-shaking feats.

A century before the Calamity, the archmage Vecna's contributions to arcane theory enabled many of the artifacts that would stoke the flames of the Calamity. He began hoarding secrets, killing those who knew them, and achieved lichdom. He conducted terrible experiments in the Verstglade for many years during this time. He amassed a force of followers and undead, disappeared with them into the Shadowfell to conquer Thar Amphala, and there built Entropis.

From Entropis, Vecna used the celestial solstice, a merging of ley energies, to open portals for his forces to attack his enemies at a whim and retreat to Thar Amphala before retaliating forces could muster. Vecna defeated one old rival, Kas, who accepted an offer of eternal life through vampirism in exchange for becoming Vecna's chief lieutenant. Vecna forged a sentient relic blade for Kas, who used it to terrorize Vecna's enemies for months, thereby becoming Kas the Bloody-Handed. Vecna, who had managed to reconstruct the Raven Queen's rites of ascension, then attempted the Ritual of Seeding to ascend to godhood. He was interrupted when the Beacon of Arms, a holy army of Pelor led by his champion Yos Varda, used a reverse-engineered celestial solstice to attack Thar Amphala. Yos Varda, Vecna, and Kas all perished, and Vecna's forces were defeated and scattered, but only a few members of the Beacon of Arms returned victorious. Vecna had left instructions for his most devoted followers to carry on the work of raising him to godhood in spite of his death; they founded the Remnants.

The Betrayer Gods return
Also inspired by the Raven Queen's ascension, Archmage Vespin Chloras sought to harness the power of the Betrayer Gods. He broke open their prison, where they had been spawning hungry creations of their own, and released them back into the Material Plane.

Driven by an urge for domination, the exiled gods came forth from their broken prisons, enthralled the mage who had freed them, and founded a kingdom of their own on the far end of the world. The kingdom was called "Ghor Dranas" (which means "gathering of shadows" in Draconic), and was located in the region which would later become Xhorhas.

Torog's followers used the caves beneath Ghor Dranas as torture dungeons, and Torog tortured the Betrayer Gods' enemies at the Bastille of Torment under the Dunrock Mountains. A warrior named Ganix attempted to strike down Torog with his army, but his army was defeated, and Torog captured and tortured Ganix, twisting him into the Laughing Hand.

Assault on Vasselheim
From Ghor Dranas, the Betrayer Gods spread their influence and eventually made an assault on the bastion of Vasselheim. The battle lasted twenty days and nights but, with the divine aid of the Prime Deities, Vasselheim and its inhabitants stood triumphant, if battered, at the end.

This assault left both mortals and gods alike shaken. Mortals turned their arcane powers to the forging of heroic weapons, and the gods prepared for war. The Betrayer Gods each forged a sentient weapon with the life force of a greater fiend: the Arms of the Betrayers.

Just before the war to come, which would be called the Calamity, followers of Zehir slaughtered the people in the Vault of Shumas and locked it off. An undead caregiver there watched over the sleeping children of Zehir, awaiting their epoch. Similarly, seers of a serpentfolk empire foresaw the Calamity; to survive its dangers, the empire created a magical stasis field under their capital city of Vos'sykriss (now Visa Isle) where its strongest people waited to one day emerge and rebuild their empire.

Possibly before or after the Calamity began
Based on descriptions of when the Calamity began, some events may have occurred before it started or during the war.
 * During a celestial solstice, elemental rifts burst open across Exandria, causing fires, earthquakes, and an outpouring of elemental monsters whom the people of the world struggled to combat. The Ashari, up to then a nomadic people, divided into four tribes to seal and watch over the rifts to the Elemental Planes of Fire (Pyrah Tribe), Water (Vesrah Tribe), Air (Zephrah Tribe), and Earth (Terrah Tribe).
 * Corellon banished Artagan to the Feywild for tricking an elven culture into worshiping a whale carcass.
 * Leylas Kryn was present when the first Luxon beacon was found.
 * The city of Shattengrod was destroyed.

The Calamity
The war that came to be called the Calamity destroyed most of civilization, and only one-third of Exandria's population survived.

The Divergence
With the Betrayer Gods defeated and banished, Melora planted the Arbor Exemplar in the Barbed Fields. The Prime Deities imposed self-exile and created the Divine Gate. Thus ended the Age of Arcanum.