Ideal Greco-Roman historiographer strove to relay information from eyewitnesses who were sufficiently involved and ideally saw the whole thing.
• Historians boasted of seeing it all “from the beginning.”
• “From the beginning” is a historiography-implying phrase.
Before writing their historical works, 1st century Greco-Roman historiographers tended to laboriously investigate the relevant issues surrounding their topics of choice.
• The works internally exemplify hard work.
• Historians imply that labor was the required norm.
• “Historia” (ἱστορία) denotes a laborious research.
• Historians testify to laboring to get info.
• Polybius calls Timaeus the laziest historian.
• Agatharchides: “old men couldn’t do it!”.
• Siculus: “Some historians die before completing!”
• Historians strove for a 1st-hand-as-possible history
In cases where witnesses were available, historians commenting on what is expected of historiography would often outright say interviewing them was required.
• Polybius etc. say “only share/relay 1st hand info”
• Plutarch etc. say “hearsay is a last resort”
• That’s wrapped into the definition of “historia” (ἱστορία).
• Historians usually stuck to writing in the witness-age.
• Historians labored to produce direct witness-based history.
Greco-Roman inquirers about the past place great value the source's being directly witness-based, or close enough.
• Ancients were oft critical thinkers.
• Polybius etc. say “all agree” 1st hand is best.
• Most inquiry in the past valued witness-testimony.
• Ancients oft said “seeing beats hearing.” • E.g. Historians oft felt 2nd-3rd hand etc. is unacceptable.
On the other hand, this counterevidence is also analyzed in the linked page:
• They didn't even prize witness testimony.
If you're following the tree, you have arrived at a circle. Otherwise, see the full page discussion here.