This is a threat on the Battle of Chalons(Battle of Catalanunian fields) where the Western Roman army and their Germanic allies under Aetius and Theodoric fought against the Huns and their Germanic allies under Atilla in the year 751. It is regarded as one of Rome's last victories.
Aetius army was believed to have about a corp of Roman Legionaires and their allies were mainly Visigoths, Alans and Franks. The Roman army in the West at this time was beleived to be under 50,000 and Aetius force was about only 20,000 available. Mainly these units were PseduoComatius recruited from border troops with maybye 5,000 to 10,000 regular Comiatus. Irregular allied forces was believed to be 40,000 in the region so for Aetius total army is about 60,000.
Huns were believed to be no more than 10,000-30,000 for the Hunnic corp due to the fact of Romans reporting the Huns as just horse archers and 30,000 is quite impossible for such a massive horse army. So maybye even only 7,000 Huns. Backed up by their allies who were mainly Ostrogoths and Gepids they were reported to have the same number as the Romans so their total army was about 60,000-70,000.
The Roman deployed their Legionaires into the center in typical battle order with cavalry on the wings. However then Aetius moves his Romans to the left flank and the Visigothic troops on the right under Theodoric. The Alans, the least trustworthy were in the center under Sangiband. Atilla confident deploys his Hunnic horse archers in the center backed up by Germanic allies the Gepids and Ostrogoths on the flanks.
The battle was domianted by a ridge and the Huns desprateley trying to take it but repulsed. Roman formed testudo I believe, and Atilla underestimated them and planned an attack on the Alans and to swing his Huns to encircle the Visigoths. Meanwhile the Gepids do not engage the Romans. Atilla charges to the center onto the Alans and routing them and planning to swing them around onto the Visigoths but the Visigoths charge in time routing the Hunnic left flank and with Romans on his left is able to encircle Atilla slightly, however darkness saves Atilla and he races back to the camp.
The battle has many myths. One myth is that the Alans didn't fully route. The Visisgoths definetley had infantry and Atilla planned to use his cavalry to encircle them. But a fully routed Alans wouldn't seem to have stopped this from happening as Atilla chased on giving both the Romans and the Visisogoths to do a counterattack. A myth is that the Alans who were reported in the 2nd century by Arrian often retreated from arrow fire but only in a feighned retreat manner. Atilla took the bait and almost got encircled.
Aetius let go of Atilla due to him believing that the destruction of the Huns would create a power vaccum as more Germanic tribes broke from Atilla. The Visigoths abandon Aetius and Aetius has no army to face Atilla. The Huns sack multiple cities later in Italy including Aquitlae. After a meeting with Pope Leo I, Atilla leaves Italy ending the Roman Hunnic War.
Was the Battle signifcant? I'd say. It stopped the Hunnic advance in Gaul forcing Atilla to change directions. And the Germans would later defeat the Huns in another battle ending their empire. It was one of the last time Rome united a conglomertion of its allies and won a victory. Did the battle effect Atilla's retreat? I'd say. The battle was described as super bloody, and is reported the Huns had horrible conditions of disease in the invasion of Italy. Also an Eastern Roman army was advancing into Danube and Atilla no longer the forces to defend his empire and attack Italy at the same time and quite possibly not enough forces to fully take and maintain Italy. Plus Italy was suffering from a crop famine.
"The Huns, who had been plundering Italy and who had also stormed a number of cities, were victims of divine punishment, being visited with heaven-sent disasters: famine and some kind of disaster. In addition, they were slaughtered by auxiliaries sent by the Emperor Marcinus and led by Aetius,(different one) at the same time, they were crushed in their [home] settlements....Thus crushed, they made peace with the Romans and all retired to their homes."
—Hydatius,