See my review on the omnibus edition.

**SPOILER ALERT** for these books, published in 1989.

In this shared world trilogy C.J. Cherryh fully exercises her history fetish by exploring the what-if inherent in the rise, fall and adaptation of cultures.
The main characters, over a timeline of nearly a thousand years, are the descendents original citizens of the Sabirn Empire, and the cultures and empires which conquer and oppose them.
In Book 1, A Dirge for Sabis, Ancaran hordes from the north (pushed by barbarians from even further north, of course – this is Cherryh) conquer the Sabirn Empire and overrun the capital, Sabis. This despite the efforts of a group of patriots including a “natural philosopher”, a smith, an army officer, and a resourceful magician to construct a weapon that could hold them off. The group of patriots are forced to flee, finding a new patron behind the Ancar lines and using their knowledge to scare off a cult fleecing the locals.
“If at first you don’t succeed, get the hell out of the way.”
Followed by Wizard Spawn
Book II of the Sword of Knowledge series
C.J. Cherryh and Nancy Asire

500 years later, (See A Dirge for Sabis) Book II concentrates on the remnants of the Sabirn people, and the scorn and persecution they suffer under the rule of the descendants of the Ancar in Sabis. This is our “one person makes a difference book”. Chemist (and alchemist) Duran rescues a Sabirn boy injured in an attack behind his shop, and is stunned to discover that his neighbors disapprove – strongly. Worse, the presence of the boy in Duran’s home leads to rumors of witchcraft and alchemical deeds that reach the ears of the court. Eventually, he flees with the boy, the boy’s grandfather, and other Sabirn who know secrets of which he could only have dreamed.

Reap the Whirlwind
Book III of the Sword of Knowledge series
C.J. Cherryh and Mercedes Lackey
(See Also, A Dirge for Sabis and Wizard Spawn) Book III brings the descendents of the protagonists of Book I and II together to resist the depredations of the Wind Clan (fleeing, in a nice bit of symmetry, the pursuit of another clan and *their* overlords). Having joined forces as a scholarly quasi-magical organization, they’re able to use the secret magics of the Sabirn, the strengths of the Ancar, the tenets of Duran, and the tenacity of the scholar’s leader to bring the Clan into alliance.

Book one shows the Cherryh touch the most clearly – the multi-layered plotting, characters who turn out to be much different than first perceived. The early chapters were clearly her work, and Leslie Fish does a great job keeping up and fleshing out the characters and story.
The next two volumes are much simpler in plot and characterization, though not without the occasional surprise. If not up to Cherryh’s, Asire’s and Lackey’s best work, still worth a read. ( )