After a four-and-a-half month siege Den Bosch surrenders to Frederick Henry on 14 September 1629. The Spanish troops withdraw from the city, and Den Bosch becomes part of the Republic. The city was entirely encircled by a 45-kilometer line. Marshes are reclaimed, trenches dug, dikes thrown up, and ramparts control the access roads. The magnitude of this enterprise, paid for by the proceeds of the Silver Fleet, is recorded in this triumphal map.