Who decided saints have halos?
Tell me about halo. How and where and when did this come about? Who decided? Why do Buddhist artifacts have halo? Who else used it?
Your wish is my command, my little swamp turnip, but you might try to be a little less peremptory next time you write your Unca Cecil, who after all has been certified by God as Font of Universal Wisdom. The halo (also called a nimbus) has been around since the time of the Greeks and Romans, and was incorporated into Christian art sometime in the fourth century AD.
The halo thing is actually pretty intricate. There are not only plain round halos, used to signify saints, there's also the cross within a halo, used for Christ; the triangular halo, used for representations of the Trinity; and the square halo, used to depict unusually saintly living personages, such as certain scandalously underpaid journalists I could name. (Square haloes, I am obliged to report, look totally Polish. No offense.) Occasionally you also see things like the hexagonal halo, about which the less said the better.
Related to the halo is the aureole, a lemon-drop-shaped item that appears to radiate from the entire body of the holy being. There's also "glory," which is sort of a generalized effusion of blessedness used to cover up troublesome details in the vicinity of the saintly centerpiece that the artist does not feel like drawing.
Similar ingenuity has been shown in the depiction of halos. In relatively crude medieval art, it was sufficient simply to sketch in a circle, but in naturalistic Renaissance art, it was deemed necessary to depict the halo in perspective, which resulted in a solid-looking object looking suspiciously like a coffee saucer suspended over the noggin of the elect. This ridiculous notion was soon abandoned in favor of rays of light and similarly mystical representations.
I note, incidentally, that in the Encyclopedia Britannica there is a picture of an angel flipping a combination halo and Frisbee, clearly an attempt at a little ecclesiastical humor. (The title sez "Angel with a Millstone," but I wasn't born yesterday.) The Buddhists of India, finally, picked up the halo from Greek invaders in the third century AD.