Retractile drawbridge explained

A retractile drawbridge is a rare type of moveable bridge in which the span is pulled away diagonally on rails. It is a variant of the retractable bridge. Only four examples are known to exist in the United States.^[1] It is believed to have been invented by T. Willis Pratt in the 1860s.

Notes and References

1. Web site: Summer Street Retractile Bridge, Spanning Fort Point Channel at Summer Street, Boston, Suffolk County, MA. Record. Historic American Engineering. www.loc.gov. en. 2019-03-26.