Christian IV's Arsenal (Danish: Christian IV's Tøjhus), is a historic building on Slotsholmen in central Copenhagen, Denmark. It was built by Christian IV of Denmark in 1604 as part of a grand scheme for the construction of a new naval harbour. The arsenal, along with several other buildings, surrounded the harbour basin which was connected to the main harbour by a narrow canal. Later, when ships became too large to enter the harbour, the fleet moved to Bremerholm and the decommissioned naval harbour was later filled in.