One of the preeminent grand theories attempting to systematise the Cosmology. The Great Flow theory suggests that all Cosmology exist in a downward spiral where all is made in Azure at the top, and all is destroyed in Abbadon at the bottom. Importantly, the River of Death exists below Materia in this hierarchy, and going even further down is described as the dissolution and ‘forgetting’ of all life and memory (beyond which nobody is believed to have been resurrected from). While travel ‘up’ the planes is possible (such as through resurrection and Divinity) it is believed that all such acts are naturally balanced out by more essence being sent down. Consequently, in some worldviews resurrection is viewed as stealing away the life and opportunities of others.
Another part of the theory states that there are two ends of this flow at the top and bottom. The top is the plane of Azure, described as light and airy, which is where everything is created. The bottom is the plane of Abbadon, dense, submerged and dark, which is where everything is eventually destroyed.
Some speculate that Abbadon loops back around into Azure.