 There is evidence of communities dating right back to the stone age with a number of burial sites in the area.It seems probable that there was a small settlement at the present location of Frederikssund in the Middle Ages but the development of the town probably began in the 12th century with the construction of a church at what was then known as Ude Sundby or Sundby Færge (Sundby Ferry).Located at a narrow point on Roskilde Fjord, Sundby Færge became the harbour for the nearby market town of Slangerup.