After Sarpsborg was burned to the ground during the Northern Seven Years' War, the ruling king, Frederik II of Denmark, decided by royal decree to rebuild the city 15 kilometres (9 mi) south of the original location. This new site's proximity to the sea and the accessible open land surrounding it made it a better location than the old one. The name Fredrikstad was first used in a letter from the King dated 6 February 1569. The temporary fortification built during the Hannibal War (1644�1645) between Sweden and Denmark-Norway, became permanent in the 1660s.
The work on the fortifications was first led by William de Coucheron and later Johan Caspar von Cicignon. During the next 60 years, several fortifications at the Fredrikstad Fortress were built, including Isegran, Kongsten, and Cicignon. In 1735, a suburb on the western side of Glomma, Vestsiden, was founded. This part later grew faster than the old city, and became the dominant city centre. Most of the buildings in the old city burned down during a fire in 1764.
In the 1840s, timber exporting from Fredrikstad started to gain momentum. In the 1860s, several steam powered saws were built along the river, and in 1879 the railway reached Fredrikstad, leading to further growth. With the decline of the timber exports as a result of the modernization of wood-processing industries in the early 1900s, Fredrikstad's production changed to other types of products. It later became one of Norway's most important industrial centres, famous for its large shipyard, Fredrikstad Mekaniske Verksted
