Mercenaries appear often in classical history, from Alxandars Crete archers to Rome Auxiliary corps. How would mercenaries get hired?

by Lukescale

How does this change into the medeival era? Early modern?

Dinocrocodile

/u/Iphikrates gave an answer to I'm an ancient Greek looking to hire mercenaries. Where do I go, and how much does it cost? that you'll probably like.