Final answer:
Early Christian art in the catacombs avoided explicit symbols like the cross due to the risk of persecution before Christianity was legalized. They used more ambiguous symbols to practice their faith in secret. Christian art became more overt with legal changes following Constantine's conversion.
Step-by-step explanation:
The lack of explicit Christian symbols such as the cross in the early Christian art found in the catacombs of Rome is primarily because the cross was a more explicitly Christian symbol than other symbols used at the time. Early Christians often had to practice their faith in secret due to the risk of persecution before Christianity became legal with the Edict of Milan. As a result, they used more ambiguous symbols that would be less likely to attract attention and that could be recognized by fellow believers while being overlooked by others. The catacombs served as both burial places and secret gathering spots for Christians, adorned with symbols like the fish (Ichthys) and the anchor, which held significance for the Christians but could be interpreted differently by non-Christians.
Earliest Christian art borrowed heavily from the existing Greco-Roman visual language but adapted it to Christian themes, often in a more symbolic rather than representational manner. Over time, Christian art became more overt, particularly after Constantine's conversion and subsequent legal changes, which made it safer to display Christian symbols openly.