Los Angeles ? Astride his own stallion, riding bareback, no stirrups, in full battle costume and helmet, historian Robin Lane Fox rode at the front in the flanking cavalry charge at Gaugamela — the one filmed in Morocco as part of Oliver Stone’s film “Alexander.”

“What immediately impresses is how your upper legs are exposed,” Fox says. “Why didn’t the Persians on the ground slice the legs off the horsemen? The Macedonians were not heavily armored. I was a sitting target, I thought. But I was not.”

And the reason, Fox thinks, comes from the ancient Greek word lyssa, meaning battle fury, madness, similar to the Old Norse term berserkr.

“I know what it means now,” Fox says. “Even with a rubber spear, I know what it means, and you don’t come near a chap, even with bare legs, if he is possessed by lyssa, especially if he is a historian.”

How do we know the details of the weaponry, tactics, force and strength of a battle that took place more than 2,000 years ago?

The life and times of Alexander were recorded in five principal histories, written by his contemporaries, men who often were eyewitnesses to the events. There was Callisthenes, a relative of Aristotle, official court historian (Alexander later had him imprisoned and perhaps tortured to death); the engineer Aristobulus; the admiral Nearchus; the flatterer Onesicritus; and, perhaps best of all, Ptolemy, a friend from boyhood, a general in his army, and later ruler of Egypt.

But there is a problem: None of these old texts survived. All the originals have been lost, and all we have are later historians, writing 300 or 400 years after Alexander’s death, quoting bits and pieces from the past in their own accounts. These histories were composed mostly by Romans, who had their own axes to grind.

“The Alexander scholarship is alive and very active around the world,” Fox says.

“There are scores of us, and there will always be,” Fox says, “because so much depends on what view one takes of the interrelations of the sources, how you compare and balance their accounts. And I dare say we underestimate the extent to which ancient authors would invent, exaggerate, fill in the gaps.”

As the Greek historian Strabo (63 B.C.-21 A.D.) remarked, “All who wrote of Alexander preferred the marvelous to the true.”