The Great Purges were the periods marked by the mass exile of all Earth-Scholars from Sanctaphrax.

The First Purge

The floating rock on which the city was built had increased in buoyancy and was threatening to break free from its moorings, and the Sky-Scholars, who disagreed with the Earth-Scholars on the proper way to avert the crisis, cast them out of Sanctaphrax and converted their Great Laboratory into the Treasury Chamber. The annual Sanctaphrax holiday known as Treasury Day was held to commemorate this event.

The Second Purge

The Second Purge happened during the Endless Winter. Again, the floating rock was threatening to break free, due to the rapidly decreasing temperatures and a chronic shortage of Stormphrax. Tension was ignited by Hax Vostillix's speech in the Hall of High Cloud, where he blamed the city's bad fortunes on remaining elements of Earth Scholarship, calling for the removal of several prominent academics whom he believed to be closet Earth Scholars. Vostillix's ideas met with great support, and he was appointed head of the Knights' Academy in place of the three 'Earth Scholar loving' Hall Masters Fenviel Vendix, Arboretum Sicklebough, and Philius Embertine. To keep order, Vostillix brought in a violent and ruthless group of guards known as Gatekeepers. Vostillix and his Gatekeepers were later defeated at the Battle of the Knights' Academy, while Quint defeated the Cloudeater which caused the Endless Winter, bringing the Second Purge to a close.