If they thought they could contain the spread of the Desolation then that sounds like the sort of thing a First Age Solar would do.
The only people who care about Places of Desolation are people using Cecelyne-based magic. If you're using sorcery or artifice and aren't bound by the surrender oaths, you can make a gateway to the desert in the middle of an oasis without compromising it's verdantness.
Exodus Passage Gates (Manse 5)
In the High first age, when creation was far larger, the exalted started to run into an issue which even their unbridled might could not overcome. There kingdoms had grown to vast.
The greatest projects of the age required exotic resources from across Creation such that even with their perfect collaboration, they would still have taken centuries to complete. But the twilight luminaries would not be denied the chance to make their visions reality, and so they found a solution. Although shackled, the endless desert still bordered all settlements in creation. If this defeated titan could be bent even further to their will, it would the unlock the distant resources required to truly reach the heights of their power in a reasonable timescale. And so, the Exodus Passage Gates came to be.
An Exodus Passage Gate is a massive arch of White Jade capped with MM resonant with the demanse it caps. The Arch rests on a perfectly flat circular dais 1000 yards in diameter on which one of the most intricate arrays of the first age was carved using only the light of the Celestial Incarne. This array contains the forces they wished to further shackle and allows the gates to be used safely.
No debris ever remains on the surface of the dais, nor will any living entity willingly cross into the area above or below it. The simple minds of animals, plants and least gods flee the distant malice, while mortals only know great danger is near. The sight of the remaining Gates in creation remain eerily pristine to the enlightened who stumble upon it.
The usage of the gates is quite simple. Each individual gate has a unique signature. When the correct gate is 'dialled', at least Resource 5 of materials resonant with the target gate essence are placed on the dais. Within moments, they dissolve into pure elemental essence and are consumed by the arch. The force of the surrender oaths binds Cecylene extorting her to make a straight path between the gates 10 days long. The essence of the demanse, and the sacrificed essence then blaze along this path forging a road bound in the laws of creation.
The Arch stays active for 1 day for every Resource 5 sacrificed to engage it.
The hazards of this road were the same as crossing a normal desert, and daemons can only enter this path through their escape conditions.
The deliberative now had the means to safely transport the resources required for their greatest works
But that was only true in the First age. The usurpation saw to that.
Now the gates stand more as a last resort.
The endless desert suffered countless indignities though the usage of these gates, and now seeks to remind any who would dare attempt their use who the strong truly are.
Without constant communication throughout creation to confirm whether gates are still intact, unused and functional, the way may lead to the middle of nowhere, leaving travellers stranded in the endless desert 5 days from the comparative mercy of her brother Malfeas.
Even then, without the expert celestials who knew the intricacies of the manse, for none survived the usurpation, the road may no longer span the 10 days, leaving travellers with a mad dash to cover the remaining distance harassed by an unshackled vindictive primordial.
Even then, without the expert celestials who knew the intricacies of the array, for none survived the usurpation, the path may no longer secure to the daemons that roam the desert, eager for the reprieve that the head of a traveller would earn from the capricious landscape.
And even then, the usage of a gate heavily drains the essence of the surrounding area, and the discharge from its use renders the surrounding area a place of desolation, without efforts to restore the essence flows of the area each gate has limited uses.
Even so, the Exodus Passage Gates are one of the few remnants of the first age that all remaining in creation seek to retain. For in this fallen age, there are threats worth risking the deserts wrath.
Whether it was the shogunate desperate to retain whatever means they could to keep creation running and ensure they could respond to threats requiring the dragons to unite, and the sidereal supporting them.
The lunars seeking a way to access all corners of creation, and the Realm seeking to inherit the shogunates mandate.
Or the returning solar seeking to recover what was lost or rebuild all of creation.