Long before other symbols of the middle ages came into existance, the Egyptians painted illuminations on papyrus scrolls.  Later, the Romans adapted these pictures, and illuminations gradually evolved to the decorations we recognize today.

An illumination is painted to brighten a document.  It can be painted in the margins, around initial letters, or can stand alone on a page.  In the middle ages, iluminations were usually of people--especially Biblical characters--or animals.  An illumination might illustrate the text, as an illustration does, or it might not.
 

In the late eighth century, Western Europeans adapted illuminations from those in Eastern Europe.  Charlemange had dictated that religious texts--including Bibles, psalters, and books of hours--must be copied by hand.  French and Italian monks, as a result, began to use illumination to break the monotony of handwritten documents.  The results of their labor were called Carolingian illuminations, after Charlemange's Latin name.  Later, in Canterbury, England, the Carolingian illuminations were combined with Celtic designs to form illuminations of the Canterbury School.

England's King Alfred began the illuminations of the Winchester School.  They were used in the late 10th and early 11th centuries.  Winchester manuscripts, such as the Benedictional of St. Aethelwold and the Arundel Psalter, featured delicately tinted figures in fluttering, draped clothing, gold, and acanthus leaf borders.
 

The monks who illuminated manuscripts often worked in groups.  They were always anonymous, as they worked because of their religion, and not for fame or fortune.  In contrast, artesians who were later commissioned to illuminate documents, such as Bibles and bestiaries and other reference works, did so to get rich, to show off their skill, or both.  The Limbourg brothers were three such artesians.

Paul, Jean, and Hermann Limbourg worked for the Duc de Berry, for whom they illuminated the "Tres Belles Heures" and the "Tres Riches Heures."   The "Tres Riches Heures" was unfinished at their death in 1416, so the twelve page document had to be finished by another artesian, Jean Colombe.

Many months were necessary to finish a manuscript.  First, the manuscript had to be copied, often in a very ornate script.  Then, illuminations had to be painted, and gold foil had to be added.

Because of their beauty, illuminations are still painted today.  Some people use the same paint and gold leaf that monks and artesians of the middle ages used, while others make woodblock prints or abstract designs.
 
 
 

"Illuminated Manuscripts." Encyclopedia Americana. v. 3.0 Grolier Educational, 1997

Carol Gerten. "Limbourg Brothers." Nov. 17, 1998 <http://sunsite.unc.edu/cjackson/limbourg/> Has a good, detailed biography of the

Limbourg brothers, and some pictures of their illuminations.

"The Vatican Library." Nov. 23, 1998 <http://sunsite.unc.edu/expo/vatican.exhibit/exhibit/a-vatican_lib/Vatican_lib.html>

A great graphics resourse (and some general information about the Vatican) but not many specifics about either illuminations in general or the individual manuscripts.