Complex sentence: At the start of the 20th century, leading architect Ernest Flagg designed the rectory, but, overall, while the 19th century saw St Mark's Church grow through its many construction projects the 20th century was marked by community service and cultural expansion.
Split into simpler sentences: At the start of the 20th century, leading architect Ernest Flagg designed the rectory. While the 19th century saw St Mark's Church grow through its many construction projects the 20th century was marked by community service and cultural expansion.