After the fall of First Ward, Praetor Keys perfected the sonic barrier technology and used it on the island area that would become Praetoria. Establishing the central island as its center, the barrier could be expanded to include all of the other islands around the lake, thus purging the whole area of Devouring Earth creatures. Once the island was secure, the refugees from First Ward started building new homes and setting up businesses. Once this was set up, the other zones soon followed.
The bulk of the Praetorian survivors live here, where the system of meritocracy gives them food, lodging, and other services depending on their contributions to the city-state. That's why the centers for education and entertainment are also located here, as well as the financial transactions and the one-and-only tailor shop.
And they continue to build as they make room for those still struggling to survive.
This zone is where Midnight Paladin spends most of his time.
(Please see its Paragon Wiki entry for more information.)