Inside Fort Frederick Maryland. An American historical interpreter is dressed in 18th century uniform from the time of the French and Indian War and the American Revolutionary War. The flag is the Maryland flag from that era. It had been in use since 1754. - The current Maryland flag was officially adopted in 1904.- The colonial era flag is named the The Calvert Arms - King's Colors or Calvert Arms - Grand Union flag. Fort Frederick was completed in 1756 after an existing design by Vauban. It's open seven days a week from Memorial Day to Labor Day and on the weekends in the spring and fall. During those times, staff and volunteers dressed in 18th century clothing demonstrate daily life in the 18th century.