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In this task, you are given a context paragraph, a question based on that and corresponding answer of a question. Your task is to generate supporting fact/knowledge from context paragraph which helps in answering a given question.

Vercingetorix was the son of Celtillus the Avernian, leader of the Gallic tribes. Vercingetorix came to power after his formal designation as chieftain of the Arverni at the oppidum Gergovia in 52 BC. He immediately established an alliance with other Gallic tribes, took command and combined all forces, and led them in the Celts' most significant revolt against Roman power. He won the Battle of Gergovia against Julius Caesar in which several thousands Romans and allies died and Caesar's Roman legions withdrew. Question: In pre-Roman Gaul the Belgic tribe of the Veliocasses or Velocasses controlled a large area in the lower Seine valley, which retains a trace of their name, as the Vexin, in 52 they raised 3000 men to support which son of Celtillus the Avernian, leader of the Gallic tribes? Answer: Vercingetorix
Output:
Vercingetorix was the son of Celtillus the Avernian, leader of the Gallic tribes.