Garth of the Allayi
This garth, or sacred garden, is a center of work, study, and devotion, as well as a focal point for the power of the Pearls and the magics of Auriga.
The Garth of the Allayi is generally a better version of the Borough Streets construction that every faction aside from the Allayi has; it has double the Dust, Science, and Influence production, comes with some Industry production, takes less away from City Approval, and even increases Food production rather than decreasing it. Additionally, it only requires one new unit of population to make a new Garth, rather than the two required for Borough Streets (though the benefit of this effect is somewhat mitigated for the Allayi due to their "We Chosen Few" trait, which doubles the amount of food needed to generate new population).
However, all of this comes at the increasing Pearl cost of each new Garth. When making a custom faction that uses Garths instead of Borough Streets, it is important to ensure that the faction will have access to enough pearls to sustain the cost of city development. The easiest way to do this is with the Allayi's Pearl Sensitive trait, since it will greatly increase the faction's income of Pearls. Another method would be to create a faction that doesn't require as much expansion; for example, The Cultists would be able to use the Garth without much trouble due to the fact that they have much less use for pearls than most other factions, as they can only build each City Improvement requiring pearls once, often resulting in the Cultists having a large stockpile of unused Pearls later in the game.