The halo was incorporated into Christian art sometime in the 4th century[citation needed] with the earliest iconic images of Christ, initially the only figure shown with one (together with his symbol, the Lamb of God). Initially the halo was regarded by many as a representation of the Logos of Christ, his divine nature, and therefore in very early (before 500) depictions of Christ before his Baptism by John he tends not to be shown with a halo, it being a matter of debate whether his Logos was innate from birth (the Orthodox view), or acquired at Baptism (the Nestorian view). At this period he is also shown as a child or youth in Baptisms, though this may be a hieratic rather than age-related representation [20]

Nativity and Transfiguration of Christ, with cross haloes; the apostles, angels and prophets have plain ones. (1025-50, Cologne).
A cruciform halo, that is to say a cross within, or extending beyond, a halo is used to represent the persons of the Holy Trinity, especially Jesus, and especially in medieval art. In Byzantine and Orthodox images, inside each of the bars of the cross in Christ's halo is one of the Greek letters Ο Ω Ν, making up ὁ ὢν — "ho ōn", literally, "the Existing One" — indicating the divinity of Jesus.[21] At least in later Orthodox images, each bar of this cross is composed of three lines, symbolising the dogmas of the Trinity, the oneness of God and the two natures of Christ. In mosaics in Santa Maria Maggiore (432-40) the juvenile Christ has a four-armed cross either on top of his head in the radius of the nimbus, or placed above the radius, but this is unusual. In the same mosaics the accompanying angels have haloes (as, in a continuation of the Imperial tradition, does King Herod), but not Mary and Joseph. Occasionally other figures have crossed haloes, such as the seven doves representing the Seven gifts of the Holy Spirit in the 11th century Codex Vyssegradensis Tree of Jesse (where Jesse and Isaiah also have plain haloes, as do the Ancestors of Christ in other miniatures).[22]
Later, triangular haloes are sometimes given to God the Father to represent the Trinity.[23] When he is represented by a hand emerging from a cloud, this may be given a halo.
Plain round haloes are typically used to signify saints, the Virgin Mary, Old Testament prophets, angels, symbols of the Four Evangelists, and some other figures. Byzantine emperors and empresses were often shown with them in compositions including saints or Christ, however the haloes were outlined only. This was copied by Ottonian and later Russian rulers. Old Testament figures become less likely to have haloes in the West as the Middle Ages go on.[24]

Pope Paschal I is depicted during his lifetime, so with a square halo, c. 820, Santa Prassede, Rome.
Beatified figures, not yet canonised as saints, are sometimes shown in medieval Italian art with linear rays radiating out from the head, but no circular edge of the nimbus defined; later this became a less obtrusive form of halo that could be used for all figures.[25] Mary has, especially from the Baroque period onwards, a special form of halo in a circle of stars, derived from her identification as the Woman of the Apocalypse.
Square haloes were sometimes used for the living in donor portraits of about 500-1100 in Italy;[26] Pope Gregory the Great had himself depicted with one, according to the 9th-century writer of his vita, John, deacon of Rome.[27] A figure who may represent Moses in the 3rd century Dura Europos Synagogue has one, where no round halos are found.[28] Personifications of the Virtues are sometimes given hexagonal haloes.[29] Scalloped haloes, sometimes just appearing as made of radiating bars, are found in the manuscripts of the Carolingian "Ada School", such as the Ada Gospels.
The whole-body image of radiance is sometimes called the 'aureole' or glory; it is shown radiating from all round the body, most often of Christ or Mary, occasionally of saints (especially those reported to have been seen surrounded by one). Such an aureola is often a mandorla ("almond-shaped" vesica piscis), especially around Christ in Majesty, who may well have a halo as well. In depictions of the Transfiguration a more complicated shape is often seen, especially in the Eastern Orthodox tradition, as in the famous 15th century icon in the Tretyakov Gallery in Moscow.[30]
Where gold is used as a background in miniatures, mosaics and panel paintings, the halo is often formed by inscribing lines in the gold leaf, and may be decorated in patterns (diapering) within the outer radius, and thus becomes much less prominent. The gold leaf inside the halo may also be burnished in a circular manner, so as to produce the effect of light radiating out from the subject's head. In the early centuries of its use, the Christian halo may be in most colours (though black is reserved for Judas, Satan and other evil figures) or multicoloured; later gold becomes standard, and if the entire background is not gold leaf, the halo itself usually will be.[31]
[edit]Decline of the halo

Fra Angelico. Coronation of the Virgin. Note the haloes of the kneeling figures at the front, seen from behind.
With increasing realism in painting, the halo came to be a problem for artists. So long as they continued to use the old compositional formulae which had been worked out to accommodate haloes, the problems were manageable, but as Western artists sought more flexibility in composition, this ceased to be the case. In free-standing medieval sculpture, the halo was already shown as a flat disk above or behind the head. When perspective came to be considered essential, painters also changed the halo from an aura surrounding the head, always depicted as though seen full-on, to a flat golden disk or ring that appeared in perspective, floating above the heads of the saints, or vertically behind, sometimes transparent. This can be seen first in Giotto, who still gives Christ the cruciform halo which began to be phased out by his successors. In northern Europe the radiant halo, made up of rays like a sunburst, came into fashion in French painting around the end of the 14th century.[32]
In in the early 15th century Jan van Eyck and Robert Campin largely abandoned their use, although some other Early Netherlandish artists continued to use them.[33] In Italy at around the same time, Pisanello used them if they did not clash with one of the enormous hats he liked to paint. Generally they lasted longer in Italy, although often reduced to a thin gold band depicting the outer edge of the nimbus, usual for example in Giovanni Bellini. Christ began to be shown with a plain halo.

Leonardo da Vinci (attributed), Benois Madonna. Floating semi-transparent haloes in perspective.
Fra Angelico, himself a monk, was a conservative as far as haloes are concerned, and some of his paintings demonstrate the problems well, as in several of his more crowded compositions, where they are shown as solid gold disks on the same plane as the picture surface, it becomes difficult to prevent them obstructing other figures. At the same time they were useful in crowded narrative scenes for distinguishing the main, identifiable, figures from the mass of a crowd. Giotto's Lamentation of Christ from the Scrovegni Chapel has eight figures with haloes and ten without, who the viewer knows they are not meant to attach a specific identity to. In the same way, a Baptism of Christ by Perugino in Vienna gives neither Christ nor John the Baptist haloes, but a saint in the background, not usually present in this scene, has a ring halo to denote his status.[34]
In the High Renaissance, even most Italian painters dispensed with haloes altogether, but in the Church's reaction to the Renaissance, that culminated in the decrees on images of the Council of Trent of 1563, their use was mandated by clerical writers on religious art such as Molanus and Saint Carlo Borromeo. Figures were placed where natural light sources would highlight their heads, or instead more discreet quasi-naturalistic flickering or glowing light was shown around the head of Christ and other figures (perhaps pioneered by Titian in his late period). Rembrandt's etchings, for example, show a variety of solutions of all of these types, as well as a majority with no halo effect at all. The disk halo was rarely used for figures from classical mythology in the Renaissance, although they are sometimes seen, especially in the classical radiant form, in Mannerist and Baroque art.
By the 19th century haloes have become unusual in Western mainstream art, although retained in iconic and popular images, and sometimes as a medievalising effect. When John Millais gives his otherwise realist St Stephen (1895) a ring halo, it seems rather surprising.[35] In popular graphic culture, a simple ring has become the predominant representation of a halo since at least the late 19th century, as seen for example in the logo for the Simon Templar ("The Saint") series of novels and other adaptations.