Towards the end of Herodotus' Histories, someone on the losing side of a fight is castrated by his sons, then crucified while those kids are stoned to death in front of him. Herodotus of Halicarnassus, "the father of history", does not blink or squirm, and does not permit a reader to do so either. Every gruesomely gory detail is evoked and underlined, but without any gratuitous moralising or editorialising. Herodotus' descriptions are often passionate, but his judgments always dispassionate.

Herodotus would not have been surprised by the Islamic State's beheadings, massacres in Rwanda, or civil wars in the Balkans, let alone the ructions during the Greek financial crisis. He knew we humans too well to expect any better of us. If Herodotus were alive today, he may well consign us to the outer darkness with his favourite pejorative term, simply dismissing us as "barbarians" (in this context, meaning non-civilised rather than merely non-Greek).

This moral clarity, rather than any nonsensical distinctions between a gullible, fantasising "father of lies" and a reliable, taciturn historian, comprises the essential difference between Herodotus and Thucydides. Every oral historian like Herodotus (a drinker at a dinner party, for instance, or a politician on the stump) relishes a shaggy-dog story, some flashes of exaggeration and embellishment, and a few digressions, in the sure knowledge that their audience does, too.

Although he has been proved right so far, Thucydides was still insufferably vain to proclaim that his history of the Peloponnesian war was "not a piece of writing designed to meet the test of an immediate public but was done to last forever". Herodotus might not have expected his own work to last forever, but he certainly expected human nature, hatreds, prejudices and frailty to do so.

Herodotus' Histories are best understood not merely as a chronicle of the victories of Greeks over Persians (during two conflicts a decade apart, in 490BC and 480BC), nor as a tribute to the victory of virtue over evil, civilisation over barbarism, or West over East. Herodotus' true subject is not episodes in human history but elements in human nature.

Marathon, Salamis, Plataea and Mycale were indisputably good battles to win. As triumphs over intolerable wickedness, they rank on the same scale as Lepanto, Gettysburg, Stalingrad or Midway. When Herodotus has the Persian emperor declare that "there will be no lands left beyond our frontiers for the sun to shine on", he tags Xerxes straight away – just like Hitler and Stalin – as a mortal enemy of any standards of decency or restraint.

Nonetheless, Herodotus' Athenian and Spartan heroes blunder and muddle along, across abysses and by uncertain tracks. Allies despise, malign and betray each other. Athenians and Spartans are united by fear in the most transient marriage of convenience, not by emotion or conviction. Herodotus pointedly emphasises that the Greeks did not win a fair fight; he makes much of the Persians' disadvantages fighting with wicker shields that were too thin, spears that were not long enough, and body armour that was too flimsy.

To cap Herodotus' scepticism about the Greeks, the hero of his narrative, Themistocles, is a sly, deft schemer, a latter-day Ulysses. He leaves fake marks on rocks and sends false messages, trapping and thwarting his allies (with more tendentious missives or threats of a separate peace) before ever doing battle with his enemies. Thucydides maintained that, under the stewardship of one of his heroes, Pericles, "the State was wisely led and firmly guarded". Of nobody would Herodotus have made such a claim.

In Herodotus, you can always be led astray by backing the wrong side. The more theatrical punishments for doing so include your eyes gouged out, your head stuck on a pike, or your hands hacked off to be left hanging on the door handles of a temple. Even the richest man in the world witnesses his son's body butchered in half, with the bits set up by the side of the road for an army to walk past.

The point in Herodotus, though, is that being a good and decent person does not really amount to much. A gallant soldier is denied any battle honours because he longed to die. A king, Candaules, is overthrown and murdered as a result of his overwhelming lust-cum-love for his own wife. The most handsome man alive is shot with an arrow between the ribs before he has struck a blow.

As flies to wanton boys are Herodotus' characters to the gods, despite the fact that those gods resemble selfish, childish villains out of a Walt Disney cartoon. Any which way you lose, might well be Herodotus' guiding principle. Oracles, too, can prove wilfully ambiguous and capricious (although Herodotus always pays them due deference). Who would be astute enough to worry about an obscure prophecy of men with long hair having their feet washed by your wives?

Winston Churchill regarded courage as the cardinal virtue, because it guaranteed all the others. Herodotus, by contrast, evidently thought that whimsy needs to be blended with courage. An emperor is saved from military disaster in Scythia only by the man with the loudest voice in the world. Spartans at Thermopylae note laconically that, if their enemies' arrows blot out the sky, they would fight in the shade. A Greek soldier from the rank and file in a trireme fights bravely, is captured, wrapped in linen, imprisoned aboard a Persian ship, then released alive and well when that ship is captured at Salamis.

Returning to the Peloponnesian war, one general interrupted a sea battle, brokered a truce, then simply rowed away, out of the story and into history. Herodotus offers few noble, placid consolations like that. The nearest he comes is when a native of Asia Minor (and Herodotus was one himself) praises his home as a place "where the sky is a more beautiful shade of blue". That whiff of lyricism is all the more heartfelt for being so rare in the Histories, but the character most likely suffers a bad end.

Mark Thomas is a Canberra-based writer.