colorful, exotic, carefully detailed descriptions of technologically advanced future periods;
the recurrent theme of the rise and fall of civilizations - both van Rijn and, later, Falkayn see that their society is doomed.
These features were reminding me of something else that I had read, in fact not just of a single other work but of an entire literary tradition in science fiction. If we trace that tradition back to its origin, then we come to this passage in the Epilogue of a classic work:
"He, I know - for the question had been discussed among us long before the Time Machine was made - thought but cheerlessly of the Advancement of Mankind, and saw in the growing pile of civilization only a foolish heaping that must inevitably fall back upon and destroy its makers in the end. If that is so, it remains for us to live as though it were not so." (HG Wells, The Time Machine, London, 1973, p. 101)
Thus, Poul Anderson's Dominic Flandry, living in his powerful but doomed future Empire, follows in the footsteps of HG Wells' Time Traveller, who visited the future but still thought cheerlessly of the Advancement of Mankind.