Lets talk mercenaries. How do I become one of them in the Classical Era? How do I find them to employ them? Was there a "ranking" system on who the best mercenary group was?

I can see the usual debate surrounding the controversy of periodization and geographical location have taken the toll on this thread, which is a shame because it's an interesting topic. For this comment I will hence limit myself to what I personally think you meant by the Classical Era. I will from now on out assume that you meant the Classical period in the Mediterranean. To be crass; all those things that has to do with Ancient Greece, Rome, the Persians and the like. I will also take the liberty to limit myself even further, because we're about to embark on an exciting adventure in the Hellenistic/Classical period together.

First we need to clarify a few things, because I can almost assure you, that what you think you know about mercenaries does not apply to this world. Usually it has been incredibly popular to assume that a mercenary of antiquity was comparable to the [condottieri] (https://en.wikipedia.org/wiki/Condottieri) of quattrocento Italy, or the Thirty Years War. Of course there is a point to be made when making this comparison, but it is misleading. Don't get me wrong people fought for money in antiquity, and they served in bands of what we could misinterpret as mercenary companies, and there were loads of them in Hellenistic times. This period was very good for business if you were a professional and skilled warrior.

So what do I mean when I imply that our traditional attitude towards mercenaries is wrong, you say? First and foremost the Greeks didn't have a word for mercenary, atleast not exactly. If you fought as a voluntary warrior you would be called either a symmachoi a philoi or xenoi which would imply in this order an ally, a friend or a guest-friend/ritualised friend. This means that all the morality(or rather lack of) implied in the concept of mercenary doesn't apply. When we talk about symmachoi, philoi and xenoi, we're talking about personal relationships. We're talking about bonds of friendships and the promise of riches as gifts from one friend to another. These friendships could be incredibly worthwhile for both parties. Entire cities could be part of these exchanges of gifts, and in turn the warriors would contribute with enormous hosts of men.

How do I become one of them in the Classical Era?

Excellent question! How do you become a mercenary in the Classical Era? The answer to this is, as many historical questions, not a simple one, but we can get an inkling about an answer from Xenophon, an incredibly interesting citizen of Athens. Xenophon experienced a great deal in his life. He became a historian, he studied under Socrates, and he was a soldier - specifically a soldier of fortune. He was an Athenian, and grew up during the Peloponnesian War, he also became a good friend of Agesilaos a king of Sparta, a city Xenophon admired dearly. His choice of employer as a soldier of fortune is interesting with the eyes of today, because Xenophon chose to serve Cyrus, the prince of Persia, and the brother of Artaxerxes II the King of Kings. He wrote about his adventures with Cyrus in the [Anabasis] (http://www.gutenberg.org/files/1170/1170-h/1170-h.htm).

Xenophon wasn't recruited directly though, neither did he seek out Cyrus himself. He joined the great expedition in another way, through the bonds of powerful friendships. It was, according to Xenophon, a friend called Proxenos that invited him to join up with Cyrus, who had been a friend of Proxenos from some other time. Proxenos promised that he would introduce Xenophon to the prince, so that he too could become a friend of the Persian. The campaign was to be against Pisidia, in Southern Asia Minor, modern day Turkey. Cyrus had invited his friends to join him in the campaign, and invited his friends to invite their friends. In turn they would be compensated lavishly. This is what was promised to Xenophon and Proxenos, but when they arrived they learnt that the campaign would go elsewhere. Because Cyrus intended to make a bid for the throne, and the campaign was to be a rebellion against his own brother, but Xenophon had now accepted the friendship of the Persian prince, and could not turn back for fear of losing his reputation and honour. So he continued even though he was deeply ashamed. He wrote that most of Cyrus friends was oblivious to the actual purpose of the campaign, excepting a single general called Klearchos that we will later visit(Anabasis 3.1.4.). This sort of friendship can almost be compared to a sort of contract, albeit one sealed in honour, and honour was a valuable commodity in ancient Greece, often more valuable than actual commodities to the members of the rich and powerful elites. So bonds of friendships are not easily broken.

As a side note, the amount of 'friends' that turned up when Cyrus called was staggering, if you think you've got a lot of facebook friends, then consider this, the host was called the Ten Thousand, he had that many 'friends'. Would you expect 10.000 friends to show up if you asked them to help you move out? There would have to be an enormous amount of pizzas in store for that to happen right?

So to answer your first question: To become a member of a mercenary group, you needed to engage in ritualized forms of friendships.

To be continued.