Anabasis means a movement upwards and can refer both to an advance and a retreat, both of which feature prominently in Xenophon's work. The Greek mercenaries who fought with the Persian Cyrus the Younger are usually referred to as The Ten Thousand although their starting numbers were closer to 12,900. After battles, the elements, and desertion, the number was 8,600 by the time the retreat reached the Black Sea.
This was a thrilling account written by a key participant just 30 years after the events. Xenophon was a leader of the Greeks, a friend of Socrates, and someone interested in how to rule and ethics. In Anabasis, we encounter Persian leadership, mad honey, clowns, and omens. It has a similar feel to Herodotus in the encounters with new peoples and an exploration of their customs. It's also fascinating to see Greek ideals come against war and real politik.