Historians are necromancers. We make the dead sit up and speak.
This is especially true of medieval historians. Modern historians have a whole lot to work with, crop yields, polling results, transcripts of Congressional debates, the amount of steel that goes into a tank. Medievalists in contrast have what people in the twelfth (or whatever medieval) century decided needed to be remembered, and therefore decided to preserve, either in a chronicle or in charters.
So our memories of the medieval past are heavily influenced by theirs. We do have archaeology to tell us more things about their material culture, but for the most part historians today have to listen to what writers in the past wanted us to hear. That is, we have to listen to the voices of the dead.
This is fine. For the most part, we would rather know how a chronicler characterized a bad harvest ("Unheard of. Horrible. God is punishing us for our sins. The people in that nasty duchy I've heard of turned to cannibalism.") than to have an exact sense of the ratio of grain harvested to grain planted.
It does mean that we have to know how to ask questions. If someone tries to ask medieval sources a question that they are not prepared to answer, one will get no reply. "What percentage of a city's streets were paved?" for example will get no answer. However, "Were cities admired for paving their streets?" or "Did city councils worry about the cost of street paving?" will get lots of answers.
The way I see it, medieval writers have been waiting for many centuries to speak. If we try to force them to answer questions they have no interest in answering, they will keep stubbornly silent. If we ask them what they would like to tell us, it will be hard to get them to shut up.
So we are necromancers, speakers to the dead. A necromancer is a kind of wizard, one who deals in dark arts. Any fiction writer is a wizard too for that matter (on which see more here), someone who can persuade readers that imaginary people who are no more than ink on a page (or pixels on a Kindle screen) are worth worrying about. Writing is an act of tremendous power. Medieval authors who made deliberate choices what to preserve in writing, on expensive parchment with laborious hand-written words, knew this. We should too.