I know there are cases of famous generals clashing and knowing each other's tactics, maybe in the case of Hannibal and Scipio, but when two massive armies battled, did most generals know who their military opponents were?
Was this based on spies, was it public knowledge?
If I were a Visigoth general fighting a Roman army, would I know the Roman general?
I know it's sort of an odd question, but it came to mind and I suppose I never really asked myself if this was commonplace. Also, please excuse me if I got any details wrong as my knowledge of history isn't very well rounded as a whole.
Thanks for reading and have a great night!
They definitely did! In some cases...
I mention Ammianus Marcellinus in a lot of my responses, but I can't help it, because his insights into the fourth-century CE military are unsurpassed. He was a high-ranking military officer in the army and can give first hand accounts of many of the battles and wars of the fourth century.
There is a clear distinction between two types of engagements in this period. There is small-scale raiding across the Rhine and Danube frontiers into Roman territory that apparently occurred every year. When these rivers froze during the winter, the barbarians were able to cross and raid Roman farms. The fact that the Roman armies returned to their barracks and garrisons in the cities during the winter assisted in making this raiding possible. Rarely are the leaders of these raids mentioned - it was most likely small, semi-independent raiding bands without significant oversight or leadership.
These raids could be a significant problem for the local populations. Ammianus relates that in 354 Julian had to save the cities of Strasbourg, Brumath, Saverne, Seltz, Speyer, Worms, Mayence, and Cologne all of which were being harassed by the barbarians. Julian fought a battle at Brumath, but no leader is mentioned for the barbarians.
The other type of engagement that Ammianus relates are the more large-scale battles and campaigns. When winter broke, the campaign season started, and the Roman emperor or generals would gather their armies to repulse any raiders in the area, and make preparations for any planned campaigns. In 357, a major battle was fought by Julian against seven kings of the Alemanni - Chonodomarius, Vestralpus, Urius, Ursicinus, Serapio, Suomarius, and Hortarius. Chonodomarius and Serapio were the foremost leaders, and Ammianus even relates that Chonodomarius commanded the left wing and Serapio the right, with the other kings commanding other sections (although there is some doubt amongst academics about how reliable Ammianus' details really are; some historians believe he added in a lot of literary embellishments).
As for what the barbarians knew of the Romans, it is hard to say. They must have known that Julian was the caesar in Gaul, but whether Serapio knew that the magister militum Flavius Severus commanded the Roman right flank against him, we can't know. The Romans definitely were not immune to having traitors and deserters give up this information to their enemies. One man, Antoninus, an official under the governor of Mesopotamia, betrayed the Empire and went over to the Persians, telling the Persian king, Shapur II, that the feared general, Ursicinus (different to the barbarian king mentioned earlier) had been withdrawn from the east. This was likely the information the spurred Shapur into marching across the frontier and besieging the Roman city of Amida, which he successfully sacked.
Hope that answered your question!