Their concept was straightforward.
Since teleportation formations don't cover enough distance between these planets, let's build space cities at the limit of teleportation formations.
Then we'd also have teleportation formations on these space cities and from them, we'll reach the target planets.
Having one single city was risky, so there was a cluster of cities around the same distance from the host planet.
Uranus had twenty such space cities that held the teleportation formation.
They weren't used normally, but when they were activated, they saved lives.
Valos was one such city.
Given their strategic importance, each of the space cities would be strictly protected by their host planet.
But Valos got the title of 'City of Depravity'.