While historical veracity may have, at one time, depended on a multitude of written historical texts as well as the "authority" of the historian, history is, thankfully, increasingly multidisciplinary:
Biologists use DNA to ground truth population dynamics in ways historians can only dream of. For example, an entire Biblical story line can be discarded as nonsense by DNA analysis of Middle Eastern peoples.
Palynologists studying lake sediments can determine a regional climate, local flora, and even determine the carrying capacity of a region for feeding it's people. Was it possible for this bronze age city to really have hundreds of thousands of citizens at the same time, despite what historical texts say?
Microscopists use sophisticated imaging techniques to ferret out invisible details from artifacts. Steadily degrading mint marks in Roman coins indicate inflation and overproduction of coins to combat it.
Hard proof that citizens were being ridden hard by their government and were very unhappy, despite whatever propaganda Cato had written to the contrary.
I love the story of how, practically overnight, nuclear chemists used carbon dating to overturn a thousand years of "expert" historical analysis that said all European culture was derived from the Greeks.
Some history may be forever unknowable, but increasingly, other disciplines are providing extremely useful tools that can verify what historians think they know and discard what is bias, propaganda, lies, fantasy, or outright nonsense.