On the Oceans of Eternity is a 2000 American science fiction novel by Canadian-American writer S. M. Stirling, the third and final book of the Nantucket alternate history series.

After making an alliance with Babylon, Hatti, and Mitanni, the Republic of Nantucket is ready to defeat Walker (who now controls Great Achaean, i.e. Mycenaean Greece) and his allies.

In the aftermath, Odikweos, who turns out to be every bit as crafty and resourceful as Homer depicted him, gains control of Great Achaean and ends the war with Nantucket.

Walker's surviving teenage daughter, already exhibiting both her father's intelligence and his ruthless determination, escaped with faithful retainers into the depths of Asia.

The Tartessians have been defeated both in a head-on invasion of Nantucket itself and in an effort to steal a march and build a hidden power base among the Native Americans of California, and for the time being they are willing to keep the peace – but their imperial dreams are far from shelved.