Page "Battle of Pharsalus" Paragraph 15

When the lines joined, Labienus ordered the cavalry to attack ; as expected they successfully pushed back Caesar's cavalry until his hidden fourth line joined in, using their pila to thrust at Pompey's cavalry and turn them to flight.

After this, Caesar ordered his six cohorts from his left flank to attack the flank of Pompey's army, the battle was more or less decided.