The artist's job is to be a witness to his time in history

Robert Rauschenberg.

I love trawling museums for inspiration. Here's a collection of free books from The Met

From Attila to Charlemagne: Arts of the Early Medieval Period in The Metropolitan Museum of Art. 26 in-depth studies of arts representing the cultures and peoples that created early Europe. Of particular interest are the essays titled The Niederbreisig Collection, and From Attila to Charlemagne.

Abbot Suger and Saint-Denis detail the life of, well, the abbot of the French abbey of Saint-Denis. He had a hand in almost everything, from inventing Gothic architecture to politics. He was a patron of the arts, and literature, and the church.

I'll be honest with you: I've not read this yet. I have heard good things about it, though, and I've set aside some time to read The Stained Glass and Metalwork part.
German Paintings in The Metropolitan Museum of Art, 1350-1600. A very narrow scope; but then again it's a catalogue. There is a total of 72 paintings in The Met, and they are all detailed here. Also, this is a selling point:

Taking us back to the turbulent times of the Reformation, it discusses the spiritual, educational, and propagandistic aims of such key personalities as Martin Luther, Erasmus, and Albrecht of Brandenburg. In its many portraits, it reflects the increased awareness of the individual in the age of humanism.

The Tale of Genji: A Japanese Classic Illuminated discusses how the book influenced Japanese culture, design, and aesthetics. It also details how the tale's transmission and reception have changed over the centuries. The book is not the actual The Tale of Genji, but that is also something that you could read.

I recommend Learning the "Women's Hand" in Heian Japan: Kana Calligraphy and The Tale of Genji.

RPG takes: In Learning the "Women's Hand"..., what immediately comes to mind for me is how people express negative things about others. Murasaki writes that Sei Shōnagon's writing of Chinese characters (which women weren't allowed to learn) "left a great deal to be desired." Not only is Murasaki a woman, so was Sei Shōnagon. We then learn that "when female characters in Genji are described as being associated with Chinese writings or customs, they are often presented in a negative light." How do we convey items like this in our own worlds?

(Above: example of hanachi-gaki, unconnected characters; it includes a single waka).

Likewise, we also see how "general knowledge" is something we need to consider. Genji says that his heart is no "shallow spring", alluding to a poem in the Man'yōshū, Collection of Ten Thousand Leaves.

Though the poem is not quoted in full, any reader of the time would have immediately understood why Genji is citing it, for it too has a connection to calligraphic education.

These are things we need to consider when players ask things. What is the knowledge that the PCs should have, but that the players aren't asking about?