Gallic War in the context of "Natural borders of France"

Commentarii de Bello Gallico (Classical Latin: [kɔm.mɛnˈtaː.ɾi.iː deː ˈbɛl.loː ˈɡal.lɪ.koː]; English: Commentaries on the Gallic War), also Bellum Gallicum (English: Gallic War), is Julius Caesar's first-hand account of the Gallic Wars, written as a third-person narrative. In it, Caesar describes the battles and intrigues that took place in the nine years he spent fighting the Celtic and Germanic peoples in Gaul who opposed Roman conquest.

The "Gaul" to which Caesar refers is ambiguous, as the term had various connotations in Roman writing and discourse during Caesar's time. Generally, Gaul included all of the regions primarily inhabited by Celts, aside from the province of Gallia Narbonensis (modern-day Provence and Languedoc-Roussillon), which had already been conquered in Caesar's time, therefore encompassing the rest of modern France, Belgium, Western Germany, and parts of Switzerland. As the Roman Republic made inroads deeper into Celtic territory and conquered more land, the definition of "Gaul" shifted. Concurrently, "Gaul" was also used in common parlance as a synonym for "uncouth" or "unsophisticated", as Romans saw Celtic peoples as uncivilized compared with themselves.

Caesar's bridges across the Rhine, the first two bridges on record to cross the Rhine river, were built by Julius Caesar and his legionaries during the Gallic War in 55 BC and 53 BC. Strategically successful, they are also considered masterpieces of military engineering.

Bibliotheca Historica (Latin; Greek: Βιβλιοθήκη Ἱστορική, Bibliothḗkē Historikḗ), also known as the Historical Library or Library of History, is a work of universal history by Diodorus Siculus. It consisted of forty books, which were divided into three sections. The first six books are geographical in theme and describe the history and culture of Egypt (Book I), of Mesopotamia, India, Scythia, and Arabia (II), of North Africa (III), and of Greece and Europe (IV–VI). In the next ten books, he recounts human history starting with the Trojan War (Book VII) down to the death of Alexander the Great (XVII). The final section concerns the historical events from the successors of Alexander (Book XVIII) down to the time of the First Triumvirate of the late Roman Republic (XL). The end of the work has been lost, and it is unclear whether Diodorus actually reached the beginning of Caesar's Gallic War in 59 BC (as he promises at the beginning of the work) or, as evidence suggests, he stopped short at 60 BC owing to old age and weariness from his labors. He selected the name "Library" as an acknowledgement that he was assembling a composite work drawing from many sources. Of the authors he used, some who have been identified include Hecataeus of Abdera, Ctesias of Cnidus, Ephorus, Theopompus, Hieronymus of Cardia, Duris of Samos, Diyllus, Philistus, Timaeus, Polybius, and Posidonius.

Diodorus's immense work has not survived intact. Only Books I–V and Books XI–XX remain in their entirety. The rest exists only in fragments preserved in Photius and in the Excerpta of Constantine Porphyrogenitus.