 Odense is one of Denmark 's oldest cities . Archaeological excavations in the vicinity show proof of settlement for over 4 @,@ 000 years since at least the Stone Age . The earliest community was centred on the higher ground between the Odense River to the south and Naesbyhoved Lake ( now dry ) to the north . Nonnebakken , one of Denmark 's former Viking ring fortresses , lay to the south of the river . Today , Odense 's Møntergården Museum has many artefacts related to the early Viking history in the Odense area . The Vikings built numerous fortifications along the river banks to defend it against invaders coming in from the coast . 
