Q. Is there a proper way to cite a classic such as Tacitus when I am using a web version without page or line numbers?
A. Tacitus’s texts are properly cited by book and section: Annales 13.32 or Historiae 5.24. If your web version doesn’t include those labels, it’s probably not a source you want to be using. More generally, however, CMOS suggests that in citing unnumbered web pages it’s sometimes possible to reference a nearby subhead, a chapter or paragraph number, or a descriptive phrase that can be searched.