Complex sentence: The Marshalsea occupied two buildings on what is now Borough High Street, the first from early in the 14th century, and possibly earlier, at what would now be 161 Borough High Street, between King Street and Mermaid Court.
Split into simpler sentences: The Marshalsea occupied two buildings on what is now Borough High Street. The first was from early in the 14th century, and possibly earlier, at what would now be 161 Borough High Street, between King Street and Mermaid Court.