In plain words, ours
Gaul is split into three parts, each held by a different people. They all differ in language, customs and laws.
All Gaul is divided into three parts, one of which the Belgae inhabit, the Aquitani another, those who in their own language are called Celts, in our Gauls, the third. All these differ from each other in language, customs and laws.
Caesar, The Gallic War 1.1Translated by W. A. McDevitte and W. S. Bohn (1869)Read the full passage (Caesar, The Gallic War 1.1, opens scaife.perseus.org)