Monastery of Gix
The monastery was home to a religious cult worshipping a machine god named Gix. In response to a dream, they travelled to Koilos and activated the portal to Phyrexia. A Phyrexian Demon stepped out, happening to bear the same name as the deity worshipped by the cult. It should be noted that whether or not the Gix worshippers were aware of Phyrexia ahead of time remains unclear. The Brotherhood of Gix, as the cult went on to call themselves, became his agents among both Urza and Mishra, manipulating both sides in the interests of Phyrexia. They succeeded in introducing Mishra to the power of Phyrexia, and he was compleated as a reward for his loyalty to his new masters. After the war, the monastery was abandoned, and the cult travelled to Phyrexia, having been turned into mechanical beings long before.
The ruins of the monastery were later used as a starting point for the construction of the Conclave of Mages during the Dark. An internal connection to Phyrexia became a bottomless pit over which Ith would be imprisoned in a cage.