I recently read Weatherford's Genghis Khan. Here is a quote from p.
238

"In a 1306 illustration of the Robe of Christ in Padua, the robe not
only was made in the style and fabric of the Mongols, but the golden
trim was painted in Mongol letters from the square Phagspa script
commissioned by Khubilai Khan. ... Old Testament prophets were
depicted holding scrolls open to long, but undecipherable, texts in
Mongol script. The direct allusion to the writing and clothing from
the court of Khubilai Khan showed an undeniable connection between
Italian Renaissance art and the Mongol Empire."

Has anyone seen these frescoes and are they scripts or just patterns?

From Weatherford's Bibliography

Tanaka, Hedemichi, "Giotto and the influence of the Mongols and
Chinese on his Art: A new analysis of the Legend of St. Francis and
the fresco paintings of the Scrovegni Chapel " Art History (Tohuko
University) vol.6 (1984)

Tanaka, Hedemichi, "Oriental Scripts in the Paintings of Giotto's
period." Gazette des Beaux-arts Vol. 113 (January - June 1989)

Other Links:

The Scrovegni Chapel, Padua

http://www.mystudios.com/gallery/giotto/preamble.html

Artistic Exchange: Europe and the Islamic World at the National
Gallery of Art, Washington

http://www.nga.gov/exhibitions/2004/artexchange/artexchange_ss1.shtm

Suzanne