Fort at Heemstede

The Fort at Heemstede was built as a defensive structure after the reclamation of the Haarlemmermeer as a Post of Krayenhoff and has been part of the Defence Line of Amsterdam since 1880.
In 1840 a start was made to drain the Haarlemmermeer and immediately a problem arose. For the defence of Amsterdam, the land had to be flooded. Between 1843 and 1848, the foundations for four forts were laid along the Ringvaart canal of the Haarlemmermeerpolder. Three tower forts were built: the Fort at the Schiphol, Fort at the Liede and at the Nieuwe Meer. The heavy buildings subsided, also due to the reclamation of the polder, so it was decided not to build a tower fort at the Fort at Heemstede, an earthen defensive structure with a moat was built there. The four fortifications were part of the Krayenhoff Posts, a forerunner of the Defence Line of Amsterdam.

Wikipedia