Books may contain primary sources. Try adding terms like these to your catalog keyword searches:
The last is most useful for ancient sources.
"A primary source is a document, image or artifact ... created contemporaneously with the event under discussion." (Williams, Historian's Toolbox, 2nd ed., p. 56)
Primary sources are evidence from participants in or eyewitnesses to an event.
Collections of printed & electronic books can be found by searching the catalog by title: