The cities appeared above the city - then named Nos Varda - during the Reaper War. Being in a stage of siege, cargo traffic to and from the city was carefully controlled to maximise protection from hostile interception, and consequently the majority of the city's freight lane holo-projectors fell into disuse. Shortly after the fall of Thessia, an unknown individual or group gained entry to this inactive portion of the Air Traffic Control network and installed a program which repurposed the lane projectors to display a series of recreations of skylines and landmark buildings from Serrice, Armali, and Dassus above Nos Varda.
Those responsible were not identified, and to this day none have come forward to claim responsibility. Although the event caused initial consternation due to the unauthorised access to ATC systems, many asari interpreted the display as a symbol of hope and defiance against the seemingly unstoppable Reapers, and almost immediately there were calls to preserve the displays once ATC regained control of the projectors. The Nos Varda Provisional Authority complied, even directing the ATC to assign a technician to maintain and augment the original program, adding many more Thessian cities to the original three. The 'sky cities', as they came to be known at this stage, became part of the NVPA's 'Thessia Lives' campaign, which used a number of private and administration-owned media outlets to spread morale-boosting messages to counteract the effect of the loss of the asari homeworld.
Following the war's end, as Nos Varda began its ongoing reorganisation and expansion into the new Nos Astra, a leaked document suggested that the Trade Directorate - under whose aegis freight traffic control fell - planned to deactivate the displays. A massive public outcry quickly produced a statement from the Board of Governors assuring citizens that the Sky Cities would be preserved, and downplaying the suggestion that any other course of action had been considered. The displays now reside over Nos Astra's tourist-oriented Vasie district (part of old Nos Varda), using dedicated projectors. Calls have been raised for cities from other worlds, including non-asari, to be added to the program, but the Communications Directorate, who took over the project once it no longer relied on freight control hardware, have so far maintained that the display is and will remain a tribute to Thessia.