The answer
The four Evangelists are the true witnesses and interpreters of Christ’s life and His salvific work. Therefore, their icons were introduced in early Christian places of worship. Usually, they are depicted on the four corners under the main dome of the nave of the church, or on the corners of the sanctuary dome, as they represent the royal pillars upon which the Lord’s kingdom was established. The icons of the apostles are on the top of the iconostasis.
Fr. Tadros Yacoub Malaty