Columbia subject headings:
Bridges--Patents.
Civil engineering--History--19th century.
Patents--United States--History--19th century.
Harvard subject headings:
Bridges--Patents.
Civil engineering--History--19th century.
Patents--United States--History--19th century.
Princeton subject headings:
Bridges--United States--Design and construction--History--19th century.
Bridges--United States--Patents.
Patents--United States--History--19th century.
Patents.