Complex sentence: A major north-south rail trunk ran parallel to the river somewhat to the west, behind the German lines, and marshy terrain leading to Lake Peipus began just north of the city, making attack difficult for either side there.
Split into simpler sentences: A major north-south rail trunk ran parallel to the river's west bank, behind the German lines. Marshy terrain leading to Lake Peipus began just north of the city, making attack difficult for either side there.