James Elroy Flecker. Early in Chapter Four of Stirling's Volume II, Marian Alston inwardly recites an entire poem which I did not recognize. However, googling soon revealed that it was by Flecker and I confirmed this from my Collected Poems of Flecker. I said that it was an indirect link. Volume I had already told us that Alston was a Flecker fan.
Anderson's Tetralogy and Stirling's Trilogy are a good contrast:
two major hard sf series;
Anderson describes Artificial Intelligence and slower than light interstellar travel in a remote future whereas Stirling describes time travel to a remote past and the initiation of a divergent timeline;
Anderson's Tetralogy is a work unto itself whereas Stirling's Trilogy is part of a longer Change series.
I recommend the Tetralogy having read it and the Change series on the assumption that it is as good as the works by Stirling that I have already read.