Set over the course of several centuries (at least), The Miracle Men is about two unimaginably good fighters. Very strong, very fast, good with any weapon, and seemingly impossible to kill, dodging before their opponent strikes, etc. In the middle ages they would fight (smaller) armies and win. They were called the miracle men because they would pull off what could only be described as miracles, enabling certain losers to be victorious. They weren't mercenaries, but were independent and unattached; they sometimes answered requests, etc. They were also enemies, equally matched. And here's the kicker: they were once the same person.
Backstory: our main character, call hime Mane, was the son of a knight, in training himself. His father was a very minor noble, but he was nobility. Mane heard stories of a magical thing (probably a chalice) which would grant people who found it power. Some investigation later, Mane set off to find it, and succeeded. He asked the thing for power, and it granted his wish on a condition: that Mane would get his power, but he would not get it unchecked (being no more specific than about that). Mane agreed, and the chalice gave him power in some manner that blinded and disoriented him during the process. When he came to again, he saw another man there which he didn't recognize but who also called himself Mane and who had all of the same memories. Using some water, they caught site of themselves and realized that they too had changed; neither looked like Mane, yet they both were.
They travelled home together, but before they could make it home their help was requested in some battle which they found easy and which started to get them fame (for their incredible skill, etc). As they tried to make their way home, they kept getting side-tracked, until on one job it was ambiguous which side was right. For some reason, Mane and Mane (who took to using different names, each giving up Mane for something else, say Peter and John) couldn't agree. Eventually when the battle was fought they were off on the sidelines fighting each other. Since they were evenly matched, neither won, and neither was really injured (they weren't big on the idea of killing each other), though they were quite impressive to watch. They tried to reconcile, once the battle was over, but they couldn't. It's quite difficult to be with someone who's exactly the same as you — it really undermines your sense of your own necessity in the grand scheme of creation — and this was the wedge which split the fissure. They split up, and sometimes fought apart, often they fought each other. To their mutual amazement, neither grew old or died.
(It turns out that the condition of checked power meant that neither could die of old age or get infirm while the other lived; and that when one was killed the other would die as well. (they could die in battle or of disease, but they wouldn't degenerate over time.) They eventually theorized something like this, during one of their truce periods, and so were especially careful not to kill each other when fighting, but limit it to wounding.)
Over the many years, they generally stayed away from each other, but occasionally during calm times would make truces with each other and talk. When you're (sort of) immortal, few people can relate, but time doesn't diminish the human need to talk to a sympathetic listiner. While they started out the same person, they grew apart from each other and changed with their different circumstances.
The main action should take place in the modern day, where their great physical ability isn't as useful any more as their vast experience and cunning (not that minor super powers aren't worth anything, but the ability to dodge arrows and kill 10 men in 10 seconds with a sword is of comparably less value when there are guns and explosives in the world; useful, but not what it once was).
As for what the modern day plot should be, good question. I'll let you know when I find out. :)