I hate to admit that every-so-often it takes my brain a moment to translate a reference century into the actual year.
Like, I was just reading the synopsis for The Northman (which looks awesome by the way), and it said that the film was set at the turn of the 10th century in Iceland. I was immediately perplexed because the movie was co-written by a native Icelander and I connected that time period of the Icelandic Commonwealth which not only didn't have a king, it didn't even have a government. I figured that a native Icelander would know that.
Then it finally clicked that the 10th century means 900AD, which was thirty years before the establishment of the Commonwealth.
Obviously, I know how all that works. Sometimes my brain just jacks off for a moment when I need to make those connections.