The Sword of Knowledge
by C. J. Cherryh

Description:
The Empire of Sabis is falling, besieged by the army of a more powerful empire and by hostile wizards. A small group of philosopher-scientists could reverse the tide if they could convince the rulers of Sabis to build the deadly new weapon that they have invented: the cannon. But when the rulers prove too short-sighted and Sabis falls, the scientists flee, disguising their knowledge under the cover of religion. Though centuries will pass and the Sabirn race will be oppressed and persecuted, the powerful knowledge will be preserved by the Order. And the time will come when only one thing stands against destruction by a ruthless and invincible barbarian horde: The Sword of Knowledge.