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.