Complex sentence: On Trajan's Column the draco is the symbolic image of victory although it is absent from pictures on the column that illustrate Trajan's second war against the Dacians, when the Romans conquered Dacia.
Split into simpler sentences: On Trajan's Column the draco is the symbolic image of the victory. However, this ensign is absent from those pictures on the column illustrating Trajan's second war against the Dacians, when Romans conquered Dacia.