The Skuldelev ships are five original Viking ships salvaged in 1957 to 1962 by the Danish National Museum from the bottom of Roskilde Fjord, in the most important of the winding natural channels called Peberrenden near the harbor of Skuldelev, c. 20 km (12 mi) north of Roskilde in Denmark. The recovered pieces constitute five types of Viking ships and have all been dated to the 11th century. They are thought to have been an early form of blockship, i.e. ships that were scuttled to block potential invasions from the sea. The numbering of the ships is slightly confusing as when the remains were unearthed, they were thought to comprise six ships, but after "Skuldelev 2" and "Skuldelev 4" were later discovered to be parts of one ship, it was decided not to renumber the other vessels.