Magisters Sidereal

"Before the might of the seven Magisters Sidereal, The Veil shattered like the flimsiest glass."

Magisters Sidereal are the seven ancient members of the Magisterium and high priests to the Old Gods, who breached the Fade physically and entered the Golden City. According to the Chantry, through their actions they committed the Second Sin and caused the First Blight, releasing darkspawn upon Thedas.

Involvement
The Old Gods began whispering to their high priests from the Fade. Dumat was the first of them to address his servant. The high priest to the God of Silence was Corypheus and it was him who put the plan to breach the gates of the Golden City in motion. Dumat tempted Corypheus to visit him in the Golden City so that he can bestow godhood onto Corypheus, for Corypheus was said to be the most powerful of the Sidereal, the most wise and the favourite of Dumat. The Conductor became obsessed with what he had heard. He shared the word of his god with other priests and acolytes of the Silence and they too became consumed with fulfilling the will of the gods. The first acolyte told Corypheus that even with all their might they will not be able to reach the Golden Heart of the Fade and suggested an alliance with the high priest of Urthemiel, the Architect of Works of Beauty.

And so the Conductor met in secret with the architect to tell him of Dumat's words. Architect found the idea of raising a mortal above the gods blasphemous and refused to help Corypheus. However, it did intrigue him and so he decided to speak to his god, Urthemiel. The God of Beauty then spoke to his own high priest and encouraged Architect to come to him in the Golden City so that he can bestow the godhood upon him instead and give him the designs to make Thedas into a paradise. And so the high priests of Dumat and Urthemiel decided to work together, each for his own agenda.

However, the power of the Conductor and the Architect were still no match against the Golden City, so they approached the remaining five of the Sidereal: the Watchman of Lusacan, the Forgewright of Toth, the Appraiser of Andoral, the Augur of Razikale, and the Madman of Zazikel. All of them craved the power of which Corypheus spoke, and so after seeking counsel with each of their chosen deity, they united under the pretense of helping Corypheus, but in reality each wanted all the power for themselves.

A hundred acolytes were chosen to gather unimaginable amounts of lyrium and slaves beyond counting in preparation for the entering of the Golden City. The lyrium and the blood sacrifices made the Veil rip open in front of them and the high priest entered the realm of the spirits with pride unmatched.

The exact sequence of events that followed did not survive to this day, as both the Andrastian Chantry and the Imperial Chantry changed the verses of the Chant of Light times beyond counting. Some sources like the Andrastian Chantry claim that the hubris of the Sidereal tainted the Golden City turning it Black, and in as punishment the Maker, a true god as opposed to the false Old Gods and the one true deity residing in the Golden City tainted them and imprisoned the Old Gods deep underground as the Archdemons; others sources state that the city was already tainted and black when the seven arrived and according to Corypheus, they did not find the Old Gods in the city, and instead the throne was empty.

In either instance, the Sidereal returned to the realm of the mortals disappointed and without the powers that were promised them. They did, however, returned with the Taint inside of them that did give them some powers similar to those of the Archdemons, such as command of the taint, shapeshifting and possession.

According to Codex entry: A Different Darkspawn?, the dwarves encountered three tall darkspawn that meet the description of the Sidereal, arguing over the failure of capturing the powers of the Golden City.