The first log boats are thought to predate both pottery and agriculture by thousands of years. During the Bronze Age, which lasted from roughly 2000 BCE to 500 BCE in Northern Europe, log boats began to change. According to Ole Thirup Kastholm, of Denmark's Roskilde Museum, the changing designs reflect broader cultural transformations.
     Examining 110 log boats recovered from sites in Scandinavia, western Europe, Britain, and Ireland, Kastholm says that starting around 2000 BCE log boats from across this vast region begin to display similarities in design. Logs were carved to have slender, vertical sides and flat bottoms that made them more stable. Many were more than 10 metres long, and some were as long as 15 metres.
     Around the same time, plank boats begin to appear. Larger and more stable than log boats, they were mainly used for ocean voyages. Traditionally, archaeologists have considered Bronze Age plank boats an exclusively British design, but Kastholm thinks plank boat technology was likely more widespread. He says the similarities between log boats found throughout western and Northern Europe shows that there was a great deal of contact between people separated by vast distances.
     The plank boats and log boats being built in northern Europe were not the most advanced watercraft of their time. Greeks, Egyptians, and other cultures around the Mediterranean Sea used sailing ships. Sails wouldn't be used in Northern Europe until the Iron Age, during the 7th or 8th century CE.
     When sails did arrive in the north, instead of copying Mediterranean designs, early Scandinavian boat builders adapted their Bronze Age plank boats. Kastholm shows that Northern European Iron Age sailing ships used the same type of cleats to secure the planks to the boat frame as the earler Bronze Age plank boats. This counters the prevailing view that the Iron Age boats came from a completely different boat building tradition. If correct, this means the Northern European tradition that produced the Viking longships had its roots in the Bronze Age plank boats.  

Edited from Hakai Magazine (20 January 2016)