Beyond the experience of the participants, I imagine ancient warfare could be hell on the landscape itself, with plenty of detritus afterwards. You'd have bodies-turned-bones of men, horses, or other animals; you'd have damaged and discarded armor or other equipment; you'd have abandoned fortifications. It seems like, given a large enough battle in a remote enough location, it could be many, many years before the landscape is returned to something like a "natural" state, to the point where it would be unrecognizable to passers-by as a one-time battlefield.
Would it have been common for travelers in the ancient world to recognize and take note of old battlefields of which they had no prior knowledge? Do we have any records of ancient authors visiting such sites and seeing traces of the fight (I'm particularly interested in the Roman and Hellenic worlds, but would be interested to hear from other places/times as well)? Or would all the "stuff" on battlefields in remote or settled areas be swallowed quickly, by nature or by human endeavor?
I didn't see any old threads on this but I'm sure someone has asked this before. Sorry if this is too broad.
In teutoberg, definitely.
Archeological evidence and contemporary histories show that the Germans left the bones of at least the Romans on the surface - possibly regarding the site in a religious context. Further, some of the Romans captured during the battle were probably tortured to death at the site and portions of their bodies were deliberately elevated for display.
In a show of strength, the Romans revisited the site many years later, were repulsed by the (to them) pagan display, and buried the remains. When they left, the archeology suggests many bodies were exhumed and their parts again scattered on the site.
Herodotus in The Histories speaks about a battle at Pelusium (525 BC) where the skulls of the Persians had been stacked up into a pile and the skulls of the Egyptians gathered into another pile to show the death count on each side many years after the battle had taken place. Herodotus himself examined the skulls and pontificated on why the Egyptians skulls were of a different thickness than the Persians.
The Classical Greeks had a tradition of setting up a trophy on the battlefield to mark their victory. This was basically a post or the trunk of a tree with some captured armour nailed to it. If you came to a place decades after a battle was fought there, you would be greeted by the trophy. This is why the careers of great generals are sometimes summed up in Greek sources as "he set up many trophies in foreign lands".
On the other hand, Cicero tells us that it was bad form to make a trophy out of lasting material (stone or metal). It had to decay over time. This might take many decades, but at least it would imply that the losing side's humiliation and slaughter would eventually be forgotten. The Thebans caused a bit of an outcry after their victory over the Spartans at Leuktra (371 BC), because they set up a trophy in stone, which has been restored and is still there now.
The rest of the stuff, however, would all be gone. Equipment was seized as plunder; bodies were completely stripped of armour and clothing. Some of this was dedicated at temples and sanctuaries, the rest sold for profit. As for the corpses, the Greeks were extremely conscientious about proper burial rites. After every battle, the losing side would request a truce to recover their dead, which the winning side was morally obliged to allow. No bodies would be left to rot on the battefield. Indeed, if they were, the generals who left them there could face brutal sanctions at home. In one famous case, six Athenian generals were condemned to death because they failed to recover some Athenian bodies after a major naval victory.
Up to the time of the Persian Wars, the dead were buried under big burial mounds, which a traveller could see if he visited the site. The one at Marathon is still there.
This is pretty much all you'd find of a former Greek battlefield, though. Unlike the Teutoburger Wald or Kalkriese, they are not very useful archaeological sites. Mostly they would return to being farmland after the survivors had cleaned up the mess.