Fortunately, there are an ample supply of things that can be used in such a game. Creatures aren’t a problem:
ape, baboon, badger, bat, bear, boar, buffalo, bull, camel, cat (wild), cattle, cheetah, crocodile, dog, dolphin, eagle, falcon, goat, herd animal, hippopotamus, horse, hyena, jackal, jaguar, lamprey, lion, men, narwhale, otter, ram, rat, rat (giant), raven, shark, skunk, snake, squirrel, stag, swan, swordfish, tiger, vulture
For character classes, we find ourselves left with the cavalier, barbarian, fighter, thief, acrobat, assassin, and if one is using the Adventures Dark and Deep rules, the mountebank and jester (minus the magical effects).
These limitations point somewhat in the direction of what adventures in such a setting would look like. No extended dungeon crawls. A lot of adventures aimed at political intrigue, social encounters, and tactical combat. Certainly something set in the Hundred Years War would do nicely. The intrigues of the Greek city states are another natural; the Peloponnesian War, for one thing. Several periods in ancient Rome suggest themselves; the Punic Wars (fighting against Carthaginian spies, perhaps), the dictatorship of Sulla, the rise of Caesar (the television show Rome would be a good guide here), or fighting incursions of Germanic barbarians, trading with them, and getting mixed up in their tribal politics on both sides of the Rhenus. Personally, I’ve never found the idea of gladiators as player characters as particularly credible, historically. They were (admittedly with notable exceptions) as a group slaves and not exactly free to go off on adventures. An entire campaign could be made around a pilgrimage to Jerusalem; fighting off pirates and bandits, dealing with hostile tribal chieftains looking to profit off the arrival of rich pilgrims, kidnappings…
Those old 2nd Edition campaign guides would be a natural benefit to such a setting. However, bear in mind that some of them aren’t strictly historical, in that they make allowances for magic (the Glory of Rome is excellent in this regard, giving options for “charlatan” mages, but others are a bit more liberal in their treatment of magic and such sections would need to be modified). Interesting question– has anyone reading this ever run a purely historical game, with no magic, using one of those books and the 2E rules?
I don’t say I’m going to be running such a game any time soon (for one thing, I’m having too much fun with my Greyhawk campaign). But I do think it would be interesting to do so, if only to point out that the AD&D rules are flexible enough, and fun enough in and of themselves, to accommodate such a campaign.