The _Vesica piscis_ (Latin, the bladder of a fish) (Plate I., Fig. 5) was used as a nimbus or glory to surround the figure of a sacred personage in sculpture and in painting. Its name shows the use of Latin terms in the Roman Church as distinguished from the Greek in _Byzantium_, which was an ancient Greek city adopted by Constantine, the Christian Emperor, as the capital of the eastern division of the Roman Empire under the new name of Constantinopolis--the modern Constantinople. But the term “Byzantine” has been retained in matters relating to art. Plate I., Figs. 15 and 16, show the Greek Cross, which is a version of the Greek letter _chi_ combined with the letter _rho_ (similar to the English _P_). This symbol represented the name Christ, and was the _Christian standard, the Labarum_, chosen by the Emperor Constantine.
Plate I., 3A. The sacred monogram generally found in church decoration stands for the Latin phrase _Jesus hominum Salvator_--“Jesus, the Saviour of men.” The Greek letters IHS (_iota, eta, sigma_) gave the first three letters of the name _Jesus_.
In the plan of an English cathedral or cruciform church, the symbol of the Latin Cross is made the basis of its form (Plate XI., Fig. 1). (The _Byzantine_ or Greek Cross has the four limbs of equal length.) The Nave, N. (Latin, _navis_, a ship, a symbol of the Church), is built from west to east. The Choir or Chancel, which is screened off by a _Cancellum_ or lattice, is in continuation of the Nave to the east end. This in some cathedrals includes the Lady Chapel, which was in mediæval times dedicated to the Virgin Mary.
In several churches and some cathedrals the head of the Cross, the Chancel or Choir, is not in line with the Nave, but is slightly inclined to one side--not in all cases the same side. Two explanations are given for this, one being its _orientation_--_i.e._, the axis of its length points to the rising of the sun on the day of its foundation, which does not coincide with that of the Nave, the Chancel having been commenced at an earlier or later date and different season of the year. The other theory is that it symbolises the head of Christ falling on one side in death.
Plate I., Fig. 14 (from the “Grammar of Ornament”), shows an ornamental design composed entirely of early Christian symbols. Plate I., Figs. 12 and 13, carved ornament and a capital bearing crude resemblance to an ancient Ionic capital. Both Figs. 12 and 13 are under the influence of Greek and Roman Art without reference to symbolism.