Arguably, the ‘key’ to conquering Persia (and so Asia) was Xenophon’s Anibasis. Xenophon was one of a large group of mercenaries hired to Cyrus, one of two princes trying to take the throne (both had claims to it). Cyrus was killed early in the battle. With the person who had hired them dead, the Greeks then just wanted to go home. The winning prince (now king) invited the officers of the group to meet to discuss leaving Persia — and murdered all of them, thinking that that would leave the now-leaderless group helpless. However, they picked some other officers by lot, including Xenophon, and they fought off the first Persian attack. With me so far? That’s just the intro.

They battled their way all the way to the Black Sea, defeating Persian armies multiple times. When they finally got home,. Xenophon wrote up a memoir, which turned into the classical-Greek version of a best seller.

Here’s the thing: It was basically a ‘how to defeat Persian armies’ manual wrapped up in an adventure story. I’ve read that it was one of Alexander’s favorite books.