For any discussion of the Great Year the work Hamlet’s Mill is an obligatory starting point. The authors of Hamlet’s Mill, the work that more or less brought the Great Year concept to the attention of modern scholarship, frame the GY in terms of a full precessional cycle. I will quote them at length, some of which will be redundant from my Author of the Month article,

and there is concealed a geometric code. That’s an example of how it works. It’s there in multiple layers, and once you realize it’s there, you realize that the whole scriptures were basically framed around this geometrical system. The allegories were devised to provide an outer, concealing covering for the inner mathematical core of the sacred writings. What it’s doing… Essentially, Sacred Geometry is the geometry of the universe. It’s the geometry of creation itself. And this was one of the secrets that these ancient master builders understood.