Creating a character
Plot and character are inextricably connected in historical fiction. It's difficult to write about them separately. In historical fiction, the gender of your character will be a primary determinant of plot possibility. Gender roles have been pretty well fixed for most of history, so while warrior women existed, they were the exception. You have to discover what were acceptable and unacceptable gender roles in the period you're writing about, and you have to respect the attitudes that went with those roles—the expectations, possibilities, and prohibitions that the culture had for men and women.
You should think long and hard about how those attitudes would have rippled out into every other aspects of life in that historical context. Your characters will be making unconscious assumptions based on their attitudes and expectations, just like we do, and those assumptions should be apparent in their speech and actions.
If you want an 8th century protagonist who's mobile and literate, you have to give that character plausible explanations for mobility and literacy. In the world I write about, literacy almost always has to involve the Church in some way. So if your character isn't a nun or a priest, he or she has to be educated by the Church, or by someone who was educated by the Church. If your character is mobile you have to justify that mobility. Travel was difficult and discouraged so unless you want your protagonist viewed with suspicion everywhere she goes you need a plausible reason to have that character on the move.
You should remember this every time you create a new character: character is the sum of who we are, and who we are is a product of the context in which we exist. There are lots of smaller contexts: family, friends, employment, education; there are greater contexts: society, culture, class, religion. Everyone has a backstory, even the guy who collects your protagonist's horse and leads it away to be fed and watered. If you want to see maybe the best example of this idea fleshed out, watch "Rosencrantz and Guildenstern are Dead," Tom Stoppard's play (and film, which Stoppard directed) showing what happens to the two relatively minor characters in Hamlet when they aren't onstage in Shakespeare's play. (They aren't drinking with my medieval detective, but they could be.)
Of course, you can't follow everyone's story because you'd never finish writing anything, but you should remember that everyone has a story of their own. The woman who scolded Alfred the Great for burning the cakes he was supposed to be watching might have been a walk-on in Alfred's story but (from her point of view) Alfred was a walk-on in her story.
Keeping in mind that humans have been human for the last 30,000 years, you can't go wrong if you attribute recognizable human emotions and motivations to your characters. Jean Auel did this in "Clan of the Cave Bear," set about 30,000 years ago at the time when Cro-Magnon and Neanderthal shared the planet. Granted, there were limited things to talk about around the campfire, but Auel wrote six volumes of the Earth's Children series propelled by the fundamental motives of love and hate, the need to belong, the urge to protect your family, jealousy, envy, and how to use a sling.
All of these characters inhabit different historical contexts and all of these characterizations respect the integrity of the fictional world and the psychological integrity of the characters' motives and cultural pressures. That's why they're three dimensional, why they engage our imaginations, and why we willingly suspend our disbelief.
The etymology of the word "character" tells us a lot about how it came to mean the qualities that define a person, which meaning, according to the Online Etymology Dictionary, it didn't acquire until the 1640s. It's from the
Middle French word carecter which meant a "symbol marked on the body." From there it traces, with slight modifications along the way, back through Old French, Latin, and Greek, to the Proto Indo-European verb for "to scrape." So character is composed of the metaphorical mark(s) scraped on a person that distinguishes her from everyone else.
With that in mind, it's easy to see how fictional characters in an historical context are informed by the scrapes and marks they acquire bumping along in the fictional reality they inhabit. These characters can be marked internally or externally, overtly or subtly, and those marks can impair or empower them, but they're all marked, just like the rest of us.
So when I created a lawyer protagonist called Hring, I had to cover him with the scrapes he'd get brushing up against the Law. Now, as far as I can tell, there were no lawyers in Anglo-Saxon England. Legal procedure was primitive and Germanic. There was no "common law" because every one of the individual Anglo-Saxon kingdoms had an individual law code, not to mention Canon Law and local custom. There were no jails so punishment took the form of fines, enslavement, mutilation, or death (unless it went to the Ordeal and God intervened). For an understanding of just how alien Anglo-Saxon law was you can download a free copy of "Essays in Anglo-Saxon Law," edited by Henry Adams.
But there was law, and even though it was recorded and influenced by the Church it originated in the secular minds of the kings and their advisors, and (bureaucracies being what they are) I imagined that there must have been a fraternity of men who helped the largely illiterate political elite of the time interpret and administer that law. So I grafted the position of advocate (thanks, Sister Fidelma) from 7th century Ireland onto 8th century Anglo-Saxon England. I'll cop to it: I made it up, but I made it up within the context of the period. The advocate in my fictional 8th century doesn't advocate for a defendant or for the prosecuting state, he advocates for the Law—he makes sure that all ritual and procedure are followed according to the applicable law codes because any deviation from the letter of the law would invalidate a case.
As an advocate, my protagonist Hring is a literate man (educated by the Church) and is steeped in the law codes of the Anglo-Saxon kingdoms as well as the Laws of the Franks. What he learned in the monastery sometimes puts him at odds with the Old Testament ethos of Anglo-Saxon law, and a feature of the stories is how he can work within the existing structure of the law to deliver justice, or as he calls it, balance.
That tension, as well as the struggle he has to reintegrate himself into his kindred after his return from the monastery, covers him with a lot of internal and external scrapes, all of which emerge from the historical context and form his character.