The Treaty of Roskilde was concluded on 26 February (OS) or 8 March 1658 (NS) during the Second Northern War between Frederick III of Denmark–Norway and Karl X Gustav of Sweden in the Danish city of Roskilde. After a devastating defeat, Denmark–Norway was forced to give up a third of its territory to save the rest, the ceded lands comprising Blekinge, Bornholm, Bohuslän (Båhuslen), Scania (Skåne) and Trøndelag, as well as her claims to Halland.After the treaty entered into force, Swedish forces continued to campaign in the remainder of Denmark–Norway, but had to withdraw from the Danish isles and Trøndelag in face of a Danish–Norwegian–Dutch alliance. The Treaty of Copenhagen restored Bornholm to Denmark and Trøndelag to Norway in 1660, while the other provinces transferred in Roskilde remained Swedish.