The Earth Book of Stormgate — Poul Anderson

One of the great modern works of the imagination, this book tells of the trader van. Rijn and the adventurer Falkayne; it rounds and completes the future history of the Polesotechnic League that spans four thousand years of Earth's interstellar empire; and it chronicles Mankind's encounters with the great-winged Ythri, who kept this record at far Stormgate.