A Benedictine monk calling himself Theophilus Presbyter between 1100 and 1120 writes the Latin treatise “De diversis artibus” (“On the Various Arts”), a practical handbook for a variety of different crafts.

In opposition to the reservations expressed by Bernard of Clairvaux concerning decoration in architecture, Theophilus ends the treatise with a panegyric on an imaginary church, decorated by a supposed pupil, which dazzles the eyes as an earthly paradise.

The work is divided into three volumes.

The first covers the production and use of painting and drawing materials (painting techniques, paints, and inks), especially for illumination of texts and painting of walls.

The second deals with the production of stained glass and techniques of glass painting, while the last deals with various techniques of goldsmithing.

It also includes an introduction into the building of organs.

Theophilus contains perhaps the earliest reference to oil paint.

It has been suggested (particularly by Eckhard Freise) that Theophilus is the same person as the artisan monk Roger of Helmarshausen.

Roger appears to have come from Stavelot Abbey in the Meuse River region, was active as an artist and author between 1100 and 1107 in St. Pantaleon's church in Cologne, and moved to Helmarshausen Abbey in 1107.

The identity of the two men has been argued among researchers for some time, but Freise's conclusions have not yet been accepted by all researchers.

Internal evidence, and his name, suggest he may have been a monk of the Eastern Roman Empire working or traveling in Northern Europe, especially Germany.