Era beginning/end
At this day, a small Atorian special forces team did, what nobody thought could be done. They infiltrated the central Portalnetwork Control Hub on Praethon and destroyed it. This led to the deactivation of all Portals and the downfall of the Old Praethorian Empire.
Following the four year decline, the Old Empire wasn't in a very good situation to beginn with, but when a small atorian special forces team infiltrated the central control hub of the Portal network on Praethon and destroyed it, it let to the final dissolution of the Old Empire. Especially during the 1000 year stagnation it developed to fully rely on all the different galaxies within the Empire and as this connection was lost, the Empire fell. The only galaxy in which the centrel authority on Praethon managed to stay in control was in Relicta itself.
To this day it is still unknown if the atorian team acted on the commands of the atorian government or on it's own.