Complex sentence: Historically there were few permanent crossings of the Trent there were only four bridges, downstream of the Tame confluence prior to the mid 18th century at Burton, Swarkestone, Nottingham and Newark.
Split into simpler sentences: Historically there were few permanent crossings of the Trent. There were only four bridges downstream of the Tame confluence prior to the mid 18th century at Burton, Swarkestone, Nottingham and Newark.