“At first I wrote about completely invented characters. Then I started writing about real-life historical figures—some of this stuff, you can’t make up if you tried.” Mary Sharratt’s fifth novel, Illuminations (Houghton Mifflin), weaves fiction into the historical record to flesh out the life and times of the 12th-century mystic and philosopher, Hildegard von Bingen who, this year, 833 years after her death, was declared a saint in the Roman Catholic Church.

Hildegard von Bingen has always been highly regarded in Germany,” says Sharratt, a Minnesota native who lived in Germany for 12 years, where she studied naturopathy and alternative therapies, worked in a clinic, and taught English. “She’s popular with both spiritual and completely secular people. You could go to medical doctors who specialize in what they call ‘Hildegard medicine.’ ”

Illuminations reads like a medieval take on Emma Donoghue’s Room. Von Bingen was only eight years old when she and a 14-year-old visionary, Jutta von Sponheim, were sealed inside a cell attached to the chapel of the Benedictine monastery at Disibodenberg, in what is now Germany. There, they were expected to live out the rest of their lives worshipping God as anchorites, a practice popular throughout Europe during the Middle Ages. When von Sponheim died 30 years later, von Bingen talked her way out of the arrangement and became the monastery’s prioress. For the next 50 years, she wrote theological, botanical, and medical texts, composed sacred music, and founded two monasteries before she died in 1179.

“The bare-bones facts are accurate,” Sharratt says of Illuminations, describing how she pored over German translations of medieval manuscripts—as well as a contemporary biography of von Bingen, entitled Vita—to piece together the story. “But obviously, I filled in the details with imagination.”

Sharratt notes that there actually are two books, both called Vita, with divergent time lines. The first, written under von Bingen’s supervision, records that she was walled up inside the cell at age eight. The other, written by von Sponheim, relates that the two girls lived with von Sponheim’s family for six years before becoming anchorites together when von Bingen was 14 years old.

“This is a radically different version, and we don’t know which one is correct. I chose Hildegard’s Vita, because that’s the most dramatic story,” Sharratt says. “I tried to put myself into Hildegard’s situation. If you were an eight-year-old, your father joined the Crusades, and your mother put you in an anchorage, how would you feel? How would you recover from that trauma?”

Illuminations is Sharratt’s second work of historical fiction: Daughters of the Witching Hill (Houghton Mifflin, 2010) takes place during the 1612 witch trials, inspired by two of its real-life victims, Mother Demdike and her granddaughter, Alizon Device. Daughters is set in the Pendle region of Lancashire, England, where Sharratt, 47, moved in 2002 with her Belgian husband, Jos Van Loo, a marketing engineer, when he was hired by a British company.

“I’ve always been passionate about history,” Sharratt says, recalling history courses she took as an undergraduate at the University of Minnesota. Sharratt graduated from there in 1988 with a degree in German studies and English literature.

It was while teaching English at a Catholic girls’ school in Innsbruck, Austria, that Sharratt began writing her debut novel, Summit Avenue (Coffee House Press, 2000). “I was living on my own in an underheated room and I didn’t have a television set...” she recalls of her novel about a young German immigrant to the Twin Cities before WWI, who finds work translating fairy tales.

Sharratt is already at work on her next historical novel with another little-known real-life woman: Emilia Bassano Lanier (1569–1645), thought to have been the “Dark Lady” of Shakespeare’s sonnets. The daughter of an Italian musician at the court of Henry VIII, Lanier was an accomplished poet, the first Englishwoman to publish a collection of poetry under her own name.

“I don’t like the lords and ladies, kings and queens kind of historical fiction that’s very popular now,” Sharratt explains. “I look for someone in the margins of history whose story just grabs me.”