The early Christians lived in a mainly pagan and hostile society. During Nero's persecution (64 A.D.) their religion was considered "a strange and illegal superstition". The Christians were mistrusted and kept aloof, they were suspected and accused of the worst crimes. They were persecuted, imprisoned, sentenced to exile or condemned to death. Unable to profess their faith openly, the Christians made use of symbols, which they depicted on the walls of the catacombs and, more often, carved them on the marble-slabs which sealed the tombs.
Like the ancient, the Christians were very fond of symbolism. The symbols were a visible reminder of their faith. The term "symbol" refers to a concrete sign or figure, which, according to the author's intention, recalls an idea or a spiritual reality. The main symbols are: the Good Shepherd, the "Orante", the monogram of Christ and the fish.
The Good Shepherd with a lamb around his shoulders represents Christ and the soul which He has saved. This symbol is often found in the frescoes, in the reliefs of the sarcophagi, in the statues and is often engraved on the tombs.
The "orante": this praying figure with open arms symbolizes the soul which lives in divine peace.
The monogram of Christ is formed by interlacing two letters of the Greek alphabet: X (chi) and P (ro), which are the first two letters of the Greek word "Christòs" or Christ. When this monogram was placed on a tombstone, it meant a Christian was buried there.
The fish. In Greek one says IXTHYS (ichtùs). Placed vertically, the letters of this word form an acrostic: Iesùs Christòs Theòu Uiòs Sotèr = Jesus Christ, Son of God, Saviour. Acrostic is Greek word which means the first letter of every line or paragraph. The fish is a widespread symbol of Christ, a motto and a compendium of the Christian faith.
Some other symbols are the dove, the Alpha and the Omega, the anchor, the phoenix, etc.
The dove holding an olive branch symbolizes the soul that reached divine peace.
The Alpha and the Omega are the first and the last letters of the Greek alphabet. They signify that Christ is the beginning and the end of all things.
The anchor is the symbol of salvation and of the soul which has peacefully reached the port of eternity.
The phoenix, the mythical Arabian bird, which, according to the beliefs of the ancient, after a thousand years arises from its ashes, is the symbol of the resurrection of the bodies.
The martyrs' tombs, the cubicles and also the arcosoliums could be at times decorated with pictures painted with the method of the fresco. The frescoes represent biblical scenes of the Old and the New Testament, some of them with a precise symbolic meaning.
The symbols and the frescoes form a miniature Gospel, a summary of the Christian faith.