Ichthys
http://en.wikipedia.org/wiki/Jesus_fish
Christian
It is believed that societies of Christians in the early Roman Empire, prior to the Edict of Milan, protected their congregations by keeping their meetings secret. In order to point the way to ever-changing meeting places, they developed a symbol which adherents would readily recognize, and which they could scratch on rocks, walls and the like, in advance of a meeting. Another story suggests that the ichthys was used as a sort of secret handshake: one person would draw with a staff a single curve, (half of the ichthys) in the sand, and another person could confirm their identity as a Christian by completing the symbol. Alternatively, one would draw the symbol, and another person would confirm their faith by drawing an eye on it.
There are several hypotheses as to why the fish was chosen. A probable explanation is that it is a reference to the scripture in which Jesus miraculuously feeds 5000 people with fish and bread (Matthew 14:15-21, Luke 9:12-17, and John 6:4-13). The ichthys may also relate to Jesus or his disciples as "fishers of men" (e.g., Mark 1:17), and may be an acronym of the Greek letters ΙΧΘΥΣ (Iota Chi Theta Upsilon Sigma) to the statement of Christian faith "᾿Ιησοῦς Χριστὸς Θεοῦ Υἱὸς Σωτήρ" (Iēsous Christos Theou Huios Sōtēr: "Jesus Christ, Son of God, Savior"). Tertullian, in his treatise On Baptism, makes a pun on the word, writing that "we, little fishes, after the example of our Icqus [ΙΧΘΥΣ] Jesus Christ, are born in water" (§1). Some sources also suggest that fish symbol was chosen because the Hebrew pronunciation of "Christ" is very similar to that of "fish" in Hebrew.
Though there is no direct evidence, the ichthys may simply be an adaptation of the mystic/mathematical symbol known as the Vesica Piscis. The length-height ratio of the vesica piscis, as expressed by the mystic and mathematician Pythagoras, is 153:265, a mystical number known as "the measure of the fish." In a biblical story in which Jesus aids his disciples to catch fish, they catch exactly 153 fish (John 21:11).
Some theories about the Historicity of Jesus suggest that Christianity adopted certain beliefs and practices as a syncretism of certain mystery religions, and this may be the origin of the Icthys into Christian circles. However, there is very little evidence of such mystery religions surfacing until after the rise of Christianity. Others posit that the Babylonian myth of Ichthys, or other similar pagan myths were adopted by Christianity, and with them the icthys sign.
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http://www.newadvent.org/cathen/06083a.htm
mong the symbols employed by the primitive Christians, that of the fish ranks probably first in importance. While the use of the fish in pagan art as a purely decorative sign is ancient and constant, the earliest literary reference to the symbolic fish is made by Clement of Alexandria, born about 150, who recommends his readers (Paedagogus, III, xi) to have their seals engraved with a dove or a fish. Clement did not consider it necessary to give any reason for this recommendation, from which it may be safely be inferred that the meaning of both symbols was unnecessary. Indeed, from monumental sources we know that the symbolic fish was familiar to Christians long before the famous Alexandrian was born; in such Roman monuments as the Capella Greca and the Sacrament Chapels of the catacomb of St. Callistus, the fish was depicted as a symbol in the first decades of the second century.
The symbol itself may have been suggested by the miraculous multification of the loaves and fishes or the repast of the seven Disciples, after the Resurrection, on the shore of the Sea of Galilee (John 21:9), but its popularity among Christians was due principally, it would seem, to the famous acrostic consisting of the initial letters of five Greek words forming the word for fish (Ichthys), which words briefly but clearly described the character of Christ and His claim to the worship of believers: Iesous Christos Theou Yios Soter, i.e. Jesus Christ, Son of God, Saviour. (See the discourse of Emperor Constantine, "Ad coetum Sanctorum" c. xviii.) It is not improbable that this Christian formula originated in Alexandria, and was intended as a protest against the pagan apotheosis of the emperors; on a coin from Alexandria of the reign of Domitian (81-96) this emperor is styled Theou Yios (Son of God).
The word Ichthys, then, as well as the representation of a fish, held for Christians a meaning of the highest significance; it was a brief profession of faith in the divinity of Christ, the Redeemer of mankind. Believers in this mystic Ichthys were themselves "little fishes", according to the well-known passage of Tertullian (De baptismo, c. 1): "we, little fishes, after the image of our Ichthys, Jesus Christ, are born in the water".
The association of the Ichthys with the Eucharist is strongly emphasized in the epitaph of Abercius, the second century Bishop of Hieropolis in Phrygia (see INSCRIPTION OF ABERCIUS), and in the somewhat later epitaph of Pectorius of Autun. Abercius tells us on the aforesaid monument that in his journey from his Asiatic home to Rome, everywhere on the way he received as food "the Fish from the spring, the great, the pure", as well as "wine mixed with water, together with bread". Pectorius also speaks of the Fish as a delicious spiritual nurture supplied by the "Saviour of the Saints". In the Eucharistic monuments this idea is expressed repeatedly in the pictorial form; the food before the banqueters is invariably bread and fish on two separate dishes. The peculiar significance attached to the fish in this relation is well brought out in such early frescoes as the Fractio Panis scene in the cemetery of St. Priscilla, and the fishes on the grass, in closest proximity to the baskets containing bread and wine, in the crypt of Lucina. (See SYMBOLISM OF THE EUCHARIST.)
The fish symbol was not, however, represented exclusively with symbols of the Eucharist; quite frequently it is found associated with such other symbols as the dove, the anchor, and the monogram of Christ. The monuments, too, on which it appears, from the first to the fourth century, include frescoes, sculptured representations, rings, seals, gilded glasses, as well as enkolpia of various materials. The type of fish depicted calls for no special observation, save that, from the second century, the form of the dolphin was frequently employed. The reason for this particular selection is presumed to be the fact that, in popular esteem, the dolphin was regarded as friendly to man.
Besides the Eucharistic frescoes of the catacombs a considerable number of objects containing the fish-symbol are preserved in various European museums, one of the most interesting, because of the grouping of the fish with several other symbols, being a carved gem in the Kircherian Museum in Rome. On the left is a T-form anchor, with two fishes beneath the crossbar, while next in order are a T-form cross with a dove on the crossbar and a sheep at the foot, another T-cross as the mast of a ship, and the good shepherd carrying on His shoulders the strayed sheep. In addition to these symbols the five letters of the word Ichthys are distributed round the border. Another ancient carved gem represents a ship supported by a fish, with doves perched on the mast and stern, and Christ on the waters rescuing St. Peter.
After the fourth century the symbolism of the fish gradually disappeared; representations of fishes on baptismal fonts and on bronze baptismal cups like those found at Rome and Trier, now in the Kircherian Museum, are merely of an ornamental character, suggested, probably by the water used in baptism.