Complex sentence: A year later, in 1708 Christopher Wren's masterpiece, St. Paul's Cathedral was completed on his birthday; however, the first service had been held on December 2,1697, more than 10 years earlier.
Split into simpler sentences: A year later, in 1708 Christopher Wren's masterpiece, St. Paul's Cathedral was completed on his birthday. The first service had been held on December 2,1697, more than 10 years earlier.