Complex sentence: As a god of motion Janus looks after passages, causes actions to start and presides over all beginnings, and since movement and change are bivalent, he has a double nature, symbolised in his two headed image.
Split into simpler sentences: As a god of motion, Janus looks after passages, causes actions to start and presides over all beginnings. Since movement and change are bivalent, he has a double nature, symbolised in his two headed image.