| Fredrikstad festning | |
|---|---|
| Fredrikstad, Norway | |
 The fortress and the city's oldest building | |
| Site information | |
| Controlled by | Norway |
| Site history | |
| Built | 1663–1666 |
| In use | 1663–1903 (fort) –2002 (garrison) |
| Battles/wars | Swedish invasion 1814 |
Fredrikstad fortress (Fredrikstad festning) was a fortification in Fredrikstad, Norway. It was the base of the Østfold Regiment, with defence related responsibilities for the east side of Oslofjord.[1]