On January 4, 46 BC, Julius Caesar defeated Titus Labienus in the Battle of Ruspina. From the article:
"Caesar vs. Titus Labienus, the traitor
The Battle of Ruspina was fought on January 4, 46 BC in the Roman province of Africa, between the Republican forces of the Optimates and forces loyal to Julius Caesar. The Republican army was commanded by Titus Labienus, Caesar’s former supporter who had defected to the Republican side at the beginning of the civil war.
Julius Caesar defeated Pompey at the Battle of Pharsalus in 48 B.C. Later that same year, Pompey was killed in Egypt. Caesar then traveled to Tunisia to battle his former lieutenant and friend, Titus Labienus.
As Labienus’s force significantly outnumbered Caesar’s, Caesar fell back onto high ground, drawing Labienus into land of his choosing. The Numidian cavalry began to wear the Caesarian troops down with missiles. This proved very effective, as the Caesarian legionaries could not retaliate. The Numidians would simply withdraw to a safe distance and keep firing. Caesar’s cavalry fought in vain to prevent being surrounded. The Caesarian troops faced a charge by the Pompeian cavalry and Numidian light troops. The Numidian light infantry bombarded the legionaries with javelins. Caesar’s legionaries threw their pila at the enemy in return, but were most ineffective. The Caesarian legionaries then huddled together in the circular orbis formation.
Titus Labienus rode up to the front rank of Caesar’s troops, coming very near in order to taunt the enemy troops. A veteran of the Tenth Legion approached Labienus, who recognized him. The veteran threw his pilum at Labienus’s horse, killing it. “That’ll teach you Labienus, that a soldier of the Tenth is attacking you”, the veteran growled, shaming Labienus in front of his own men. Some men however began to panic. One aquilifer panicked and attempted to flee. Caesar grabbed the man, spun him around and shouted “the enemy are over there!”.
Caesar gave the order to make the battle line as long as possible. He ordered that every second cohort to turn around, so the standards would be facing the rear. The legionaries charged and threw their pila, scattering the Pompeians. They pursued their enemy for a short distance, and began to march back to camp. However Marcus Petreius, and Gnaeus Calpurnius Piso appeared with 1,600 Numidian cavalry and a large number of infantry. The Caesarians were surrounded. They might have formed the testudo for protection. The Caesarians got ready for another breakout. They successfully broke out, but then both armies slowly retired to their camps.
The battle was a bloody affair, with Caesar losing as much as one-third of his forces. Caesar would again face Optimate forces three months later in the Battle of Thapsus, eventually achieving victory.
Ruspina is located in modern day Tunisia."