Philadelphia's history of tall buildings is generally thought to have begun with the 1754 addition of the steeple to Christ Church, which was one of America's first high-rise structures. Through most of the 20th century, a "gentlemen's agreement" prevented buildings from rising higher than the 548-ft (167-m) Philadelphia City Hall. Despite this, Philadelphia amassed a large collection of high-rise buildings. The completion of One Liberty Place in 1987 broke the agreement, and Philadelphia has since seen the construction of ten skyscrapers that eclipse City Hall in height.