Christianpris, Naval fortress in Kiel, Germany

Christianpris, now Festung Friedrichsort, is an irregular pentagonal sea fortress with five bastions, built on a land tongue at the narrowest point of Kiel Fjord. It was ringed by a water moat, of which the southern and eastern sections survive, along with ramparts on the south, west and east. The site measures about 300 m across; the main area is fenced and entered through a gate.

King Christian IV commissioned its construction in 1632 as a defense against Swedish forces during the Thirty Years War. It was renamed Festung Friedrichsort in 1663 and served as a key military installation through the 19th century.

The name Christianspries honoured King Christian IV, who founded the fortress in 1632; after its rebuilding from 1663 it was renamed Friedrichsort for Frederick III. From the 17th century a postman and a boatman carried mail between Kiel's old town and the fortress. Today the site is Kiel's only gated community, fenced and entered through a gatehouse, and its buildings are used mainly by businesses, some from the creative sector.

The fortress has been privately owned since 2006, and the main area is fully fenced and reached through a gate; entry is only possible on a guided tour. The site is surrounded by a dike built to protect the low-lying land, and the southern and eastern moat plus the ramparts in the south, west and east survive. The western moat was filled in 1965 for the neighbouring MaK plant, and the north-eastern bastion was removed in the late 1950s to create an access road.

The fortress served as the testing ground for the first working maritime mines during the Schleswig-Holstein uprising of 1848. This development became a turning point in how navies around the world approached coastal defense.