Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 6. Christian Art” (Includes sections 75-81).
§ 78. Other Christian Symbols.
Schaff notes that many other symbols were used in Christian art and worship, mostly borrowed from Scripture, such as doves, olive branches, and the like (Schaff 2014, Loc. 15710). He lists many and their significance.
§ 79. Historical and Allegorical Pictures.
It was a natural development to depict scenes from the Bible in artwork (Schaff 2014, Loc. 15721). We begin to see these by the third century. Schaff notes that mythological figures also appear sometimes, possibly by the influence of Gnosticism (Schaff 2014, Loc. 15727). Jesus as the Good Shepherd is a popular figure, as is Orpheus (Schaff 2014, Loc. 15744). Schaff theorizes that Orpheus’ popularity was related to his frequent depiction as a musical storyteller.