The second-century Christian teacher Clement of Alexandria identified a dove, a fish, a ship, a lyre, and an anchor as suitable images to be engraved on Christians’ signet-rings (or seals). Archaeologists have discovered a gold finger-ring from the third or fourth century that depicts an anchor, cross, lamb, shepherd, dove, and the abbreviation for Christ.
Some early Christians made the Greek word for fish, ichthus, into an acronym for “Jesus Christ, God’s Son, Savior.” Tertullian, a theologian writing at beginning of the third century, interpreted this practice as a symbol of baptism: “But we small fishes, named after our great ICHTHUS, Jesus Christ, are born in water and only by remaining in water can we live.”
The symbol of the anchor, with its crossbar, resembles a cross. An anchor and two fish (probably from the third century) occur together on a grave slab in the catacomb of Domitilla in Rome.
Justin Martyr, a Christian apologist writing in the 150’s–160’s, argued that God had providentially put the shape of the cross in everyday objects, such as the masts of ships, tools like the plough and the axe, and the standards of Roman legions. Christians would often pray standing up with their arms stretched out in the form of a cross. As early as the 200’s, Christians were making the sign of the cross with their hands. The cross was so important that pagans charged Christians with worshipping the cross.