Beginning of the 5th century
Cast taken from a sarcophagus in the Basilica of Santi Quattro Coronati, Rome
Pio Christiano Museum, the Vatican
Two soldiers with shields flank a "staurogram," a ligature of the Greek letters T and P that represents the crucified Christ. The A and W are the Greek "alpha and omega" of Revelation 22:13, where in Heaven Christ says, "I am Alpha and Omega, the first and the last, the beginning and the end" (c.f. 1:8 and 21:6).
The two soldiers are probably the guards who were at the tomb at the Resurrection (Matthew 27:62 - 27:4). Thus the import of the whole composition is to abstract and theologize the death of Jesus, moving the mind of the viewer from it to the Resurrection and thence to his glorification in Heaven.
The center panels of the Sarcophagus of Domatilla and the Passion Sarcophagus with St. Peter (both mid-4th century) similarly harmonize Christ's death, resurrection, and glory – but using a chi-rho symbol instead of a staurogram.
This image in full resolution
More of the staurogram
More of the Crucifixion
Photographed at the museum by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.