Complex sentence: Fort Fareham, Fort Wallington, Fort Nelson, Fort Southwick, Fort Widley, Fort Purbrook were built in the 19th century and designed to protect Portsmouth from an inland attack.
Split into simpler sentences: Fort Fareham, Fort Wallington, Fort Nelson, Fort Southwick, Fort Widley, and Fort Purbrook. These were built in the 19th century and designed to protect Portsmouth from an inland attack.