Clermont ranks among the oldest cities of France. The first known mention was by the Greek geographer Strabo, who called it the "metropolis of the Arverni" (meaning their oppidum, civitas or tribal capital). The city was at that time called "Nemessos" – a Gaulish word for a sacred forest, and was situated on the mound where the cathedral of Clermont-Ferrand stands today. Somewhere in the area around Nemossos the Arverni chieftain Vercingetorix (later to head a unified Gallic resistance to the Roman invasion led by Julius Caesar) was born around 72 BC. Also, Nemossos was situated not far from the plateau of Gergovia, where Vercingetorix repulsed the Roman assault at the Battle of Gergovia in 52 BC. After the Roman conquest, the city became known as "Augustonemetum" sometime in the 1st century, a name which combined its original Gallic name with that of the Emperor Augustus. Its population was estimated at 15,000–30,000 in the 2nd century, making it one of the largest cities of Roman Gaul. It then became "Arvernis" in the 3rd century, taking its name, like other Gallic cities in this era, from the people who lived within its walls.