Unless you happen to be an authority on medieval theology, it's unlikley that you've heard of Rabanus Maurus (780–856). Maurus was one of the most renowned scholars of his day, as well as being a Benedictine abbot, the Archbishop of Mainz, Germany, and a theologian. He wrote treatises on education, poems, sermons, and is credited as being influential in the development of the German language.
He also created mathematical and geometric poems, most of which apply the Christian cross as an organizing structure and are collectively known as De laudibus sanctae crucis. Maurus' work can be found on this website of the Bibliothèque Nationale de France. Additional illustrations and details here.