In ancient sources, the Greek terms εἰκών and its diminutive εἰκονίδιον, which means “little painting,” were used for both pagan and Christian panel paintings.

Christians decorated walls of their first places of worship, catacombs, initially with symbols (e.g. the cross, lamb, fish, and dove), and from the 3rd century CE, with figurative images made in fresco technique that were called icons. The oldest examples are preserved in Dura-Europos (present-day Salahiyeh) in Syria and in Roman catacombs. They thematica…