Complex sentence: The footbridges were brought forward and the river crossed with ease but, the divisional history comments, the "railway embankment on the far side was a much greater natural obstacle" due to heavy rain and was "heavily wired" and defended.
Split into simpler sentences: The footbridges were brought forward and the river crossed with ease. However, the divisional history comments, the "railway embankment on the far side was a much greater natural obstacle" due to heavy rain and was "heavily wired" and defended.