Christ or Marx?

Rome Open City portrays (even celebrates) the alliance during the Resistance between the Catholics (exemplified by Don Pietro) and the Marxists (exemplified by Manfredi) to combat the Nazis.  Both groups set aside their ideological differences and suffer together in the process.  But what is the ideology behind this movie?  What is the meaning of this suffering?  Is it the Christian idea of redemptive suffering in which an omnibenevolent God turns suffering into joy?  Or is it the Marxist idea that suffering is part of the dialectic of history leading to the inevitable Marxist state?  There are several examples of Christian iconography in this film: images of a pieta (Mary holding her dead son), crucifixion, and sacrificial lambs.  Do these images indicate a Christian interpretation of the film -- or can they be interpreted in a more secular way?  Is this a Christian or Marxist film -- or are these categories too simplistic?