Former University professor and renowned art historian Ernst Kitzinger died of a stroke in his Poughkeepsie, New York home on Jan. 22. He was 90.

“He put the study of Medieval and Byzantine mosaics on the scholarly map of American art history,” said Christine Kondoleon, a close friend and the curator of Greek and Roman art at Boston’s Museum of Fine Arts.

His work embraced the full range of late antiquity and early medieval art, from Anglo-Saxon Northumbria through Rome to Byzantium, according to a family-issued obituary.

“Essentially, he was one of the last generation of great German art historian emigrés,” said Alice Mary Talbot, the director of Byzantine studies at Dumbarton Oaks—a Harvard research library in Washington, D.C. “It was as Walter Cook, director of the Institute of Fine Arts of New York University, once remarked: ‘Hitler shook the tree, and I gathered up the fruit as it fell.’”

Kitzinger fled to England from Nazi Germany in 1935, where he settled into a job as an unpaid assistant at the British Museum.

After the Battle of Dunkirk, though, he was interned as an enemy alien and shipped to Australia.

“While on the ship to Australia he taught himself Russian,” Kondoleon, a former student, said. “I was particularly inspired by his complete commitment to Byzantine studies despite the challenges he faced.”

Upon his release in 1941, Kitzinger traveled to the U.S. to work as a junior fellow at Harvard’s newly created Center for Byzantine studies at Dumbarton Oaks.

Except for a brief absence spent serving with the Office of Strategic Services in Washington and London, Kitzinger remained at Dumbarton Oaks for 22 years, and served as director of Byzantine studies from 1955 until 1967.

“He was one of the intellectual founders of Dumbarton Oaks,” Talbot said. “He wasn’t the first director, but he was there during a reasonably formative period and played a key role in developing its library, nurturing the fellowship program, organizing symposia and in supervising publications.”

In 1967, Kitzinger took up a post nearer Harvard Yard as the Arthur Kingsley Porter University Professor.

He remained at Harvard in this capacity until his retirement in 1979.

Although a quiet and “august” professor, Kitzinger’s students said he was respected as a researcher and orator.

“Each lecture was like a jewel in its crystalline clarity and precision,” Kondoleon said. “Students would applaud after each lecture, impressed by the elegance of the presentation.”

His reputation for clarity was matched only by his reputation for rigor.