How many books are included in Pliny the Elder's lost work about the history of German wars?

Pliny the Elder’s lost work concerning the history of the German wars is believed to have originally consisted of 20 books. This estimate comes from references made by ancient authors and the context of Pliny’s extensive scholarship, which included a range of topics in natural history and ethnography. A document of this scale would have been consistent with the detailed and systematic nature of his approach to documenting history and cultures.

In this context, the number 20 signifies a significant attempt by Pliny to cover a wide array of events and insights related to the Germanic tribes and their interactions with Rome. This lost work emphasizes not only the historical but also the geographic and cultural dimensions of the Germanic territories as understood in Pliny's time. The volume of books indicates an exhaustive inquiry typical of a Roman elite scholar, providing a broad scope of information and analysis that would serve historians and contemporaries interested in military affairs and ethnography.

Other answer options suggest fewer or more books, which do not align with the historical context or extant references made about Pliny’s endeavors.