Early Christian Art
While Christianity could be argued to have started somewhere between the years 1 and 33 AD, it was not the official religion of the Roman Empire until the Edict of Milan in 313 AD, though by then it had extended throughout the empire and its social structure, thus necessitating the official conversion. So during its early years, it had to practiced in secret, and its art created in secret, independent of any stylistic influences of the time. As it became more established, there was a reaction against the pagan art of the Romans, and Christian art intentionally continued in a different style in order to differentiate itself. While Greco-Roman art was very idealized and aesthetically pleasing, medieval Christian art leaned away from realistic depictions and instead relied on subject matter and symbolism, and therefore concept as its basis. Figures became more abstracted in sculpture and painting, though not for lack of skill on the part of the artists. As the third dimension was denied, the art was more spiritualized, and was meant to be understood as a picture, rather than a direct representation. This style dominated Early Christian works.
Early Christian art was already emerging by the second century AD and could be found in cemeteries and catacombs, and not places where large amounts of people could gather at the same time to look. An example of this is the Good Shepherd ceiling painting in the Catacomb of Saints Peter and Marcellinus in the 4th century AD. As Christianity was still illegal at the time, the great Greco-roman artists were not the ones making the art. Rather, it was made by regular people with some amount of artistic ability, and had to be made so that they wouldn't get caught and tossed to the lions. The art had to be made in a way so that it would not immediately stand out as Christian and tip off the Romans. What emerged was an idea of a coded representation, using images already used in classical symbology, such as the depiction of Christ as a shepherd, Mary with the Christ child, poses of prayer, Christ in the temple teaching, and so on. Only other Christians, people familiar with the gospels, would be able to correctly identify the subject matter as Christian. Along with scenes from the gospels were images from the Hebrew Bible, which was used to add additional support to the gospels and happened to contain numerous things that could be transferred into art, which were.
The conversion of Constantine and the empire to Christianity allowed the making of Christian images to leave the deep, dark catacombs of the city limits. The Triumphal Arch of Constantine, built next to the Coliseum in Rome circa 313 AD, combined both Roman architectural forms with Christian reliefs. The arch was built to commemorate a military triumph but symbolized the triumph of Christianity. The shape was the same as normal arches, which later became imitated in the shape of Christian churches. There were both old Roman reliefs taken from other monuments, along with new reliefs commissioned which copied the style of the secret Christian catacomb paintings, deliberately creating a stylistic link between the two and making a distinct contrast with the Greco-roman pagan style. The juxtaposition of the old and new forms symbolized the continuation of the institution of the Empire and its authority along with the new church.
The stylistic differences between classical forms and the new Christian style continued into portraiture. The head of statue of Constantine from the early 4th century reflects these changes. Just as the figures on the sarcophagus of Junius Bassus were of a static and less idealized style, the portrait of Constantine differs from earlier Roman portraits by its more abstracted elements. The former were very precise and individualized, while the latter, as was the continuing trend in Christian art at the time, was more abstracted and therefore more about symbolism than personality.
As Christian art continued to develop, it moved further and further away from the classical style, as early Christians did not want their characters to be mistaken for pagan subjects. Anything associated with the pagan world was considered sinful. Nude statues were destroyed, as idealized or beautiful depictions of the body were also regarded as sinful. And example of this development is the sarcophagus of the politician Junius Bassus from 359 AD. Although Christ is depicted beardless and idealized, he's the only one. Adam and Eve, while nude, are in no way depicted in an idealized or attractive way, and everyone else is fully dressed and draped in such a way that their bodies are hardly even noticeable.
With the legalization of Christianity and its establishment as the official state religion, churches were needed to hold all the new worshippers. Previously, Christians could not safely establish a permanent meeting place anywhere except perhaps in the far fringes of the Empire, and these few were not built with permanence in mind, as none have survived to today. Unlike the old Roman religion, Christians needed a space to gather together to worship in much larger groups, so now that it was the religion du jour, new spaces for all the new Christians needed to be found The basilica plan, a Roman style building designed to hold large crowds for law courts and other official activities, ended up being used, and its design with three aisles and a semicircular apse became the standard for Christian churches. This was not a conscious decision; instead, the early Christians simply gravitated towards that style and the symbolism just worked out in their favor. Along with being a convenient shape, symbolism played a part yet again in the choice, as the design reflected the authority that the basilica represented and transferred it into the architecture of the church. Old St. Peter's in Rome was built between 324 and 350 according to this plan and became the seat of Papal power. Another style of church was the circular plan, such as that of Santa Costanza in Rome. Smaller than the Basilica plan, it features a round plan and a dome, the dome symbolizing heaven and the circle symbolizing eternity, two important features of the religion.